by Matt Macy as well as other changes which he has accepted via pull
request to his github repo at https://github.com/mattmacy/networking/

This should bring -CURRENT and the github repo into close enough sync to
allow small feature branches rather than a large chain of interdependant
patches being developed out of tree.  The reset of the synchronization
should be able to be completed on github by splitting the remaining
changes that are not yet ready into short feature branches for later
review as smaller commits.

Here is a summary of changes included in this patch:

1)  More checks when INVARIANTS are enabled for eariler problem
    detection
2)  Group Task Queue cleanups
    - Fix use of duplicate shortdesc for gtaskqueue malloc type.
      Some interfaces such as memguard(9) use the short description to
      identify malloc types, so duplicates should be avoided.
3)  Allow gtaskqueues to use ithreads in addition to taskqueues
    - In some cases, this can improve performance
4)  Better logging when taskqgroup_attach*() fails to set interrupt
    affinity.
5)  Do not start gtaskqueues until they're needed
6)  Have mp_ring enqueue function enter the ABDICATED rather than BUSY
    state.  This moves the TX to the gtaskq and allows processing to
    continue faster as well as make TX batching more likely.
7)  Add an ift_txd_errata function to struct if_txrx.  This allows
    drivers to inspect/modify mbufs before transmission.
8)  Add a new IFLIB_NEED_ZERO_CSUM for drivers to indicate they need
    checksums zeroed for checksum offload to work.  This avoids modifying
    packet data in the TX path when possible.
9)  Use ithreads for iflib I/O instead of taskqueues
10) Clean up ioctl and support async ioctl functions
11) Prefetch two cachlines from each mbuf instead of one up to 128B.  We
    often need to parse packet header info beyond 64B.
12) Fix potential memory corruption due to fence post error in
    bit_nclear() usage.
13) Improved hang detection and handling
14) If the packet is smaller than MTU, disable the TSO flags.
    This avoids extra packet parsing when not needed.
15) Move TCP header parsing inside the IS_TSO?() test.
    This avoids extra packet parsing when not needed.
16) Pass chains of mbufs that are not consumed by lro to if_input()
    rather call if_input() for each mbuf.
17) Re-arrange packet header loads to get as much work as possible done
    before a cache stall.
18) Lock the context when calling IFDI_ATTACH_PRE()/IFDI_ATTACH_POST()/
    IFDI_DETACH();
19) Attempt to distribute RX/TX tasks across cores more sensibly,
    especially when RX and TX share an interrupt.  RX will attempt to
    take the first threads on a core, and TX will attempt to take
    successive threads.
20) Allow iflib_softirq_alloc_generic() to request affinity to the same
    cpus an interrupt has affinity with.  This allows TX queues to
    ensure they are serviced by the socket the device is on.
21) Add new iflib sysctls to net.iflib:
    - timer_int - interval at which to run per-queue timers in ticks
    - force_busdma
22) Add new per-device iflib sysctls to dev.X.Y.iflib
    - rx_budget allows tuning the batch size on the RX path
    - watchdog_events Count of watchdog events seen since load
23) Fix error where netmap_rxq_init() could get called before
    IFDI_INIT()
24) e1000: Fixed version of r323008: post-cold sleep instead of DELAY
    when waiting for firmware
    - After interrupts are enabled, convert all waits to sleeps
    - Eliminates e1000 software/firmware synchronization busy waits after
      startup
25) e1000: Remove special case for budget=1 in em_txrx.c
    - Premature optimization which may actually be incorrect with
      multi-segment packets
26) e1000: Split out TX interrupt rather than share an interrupt for
    RX and TX.
    - Allows better performance by keeping RX and TX paths separate
27) e1000: Separate igb from em code where suitable
    Much easier to understand separate functions and "if (is_igb)" than
    previous tests like "if (reg_icr & (E1000_ICR_RXSEQ | E1000_ICR_LSC))"

#blamebruno

Reviewed by:	sbruno
Approved by:	sbruno (mentor)
Sponsored by:	Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D12235