The modification to the hash are already naturally locked by
in_control_sx.  Convert the hash lists to CK lists. Remove the
in_ifaddr_rmlock. Assert the network epoch where necessary.

Most cases when the hash lookup is done the epoch is already entered.
Cover a few cases, that need entering the epoch, which mostly is
initial configuration of tunnel interfaces and multicast addresses.

Reviewed by:		melifaro
Differential revision:	https://reviews.freebsd.org/D32584