This reverts commit 2886c93d.
The original commit has two problems:

* It sets SO_SNDBUF to be as large as MAXLINE.  But for unix domain
  sockets, the send buffer is bypassed.  Packets go directly to the
  peer's receive buffer, so setting and querying SO_SNDBUF is
  ineffective.  To ensure that the socket can accept messages of a
  certain size, it would be necessary to add a SO_PEERRCVBUF socket
  option that could query the connected peer's receive buffer size.

* It sets MAXLINE to 8 kB, which is larger than the default sockbuf size
  of 4 kB.  That's ok for the builtin syslogd, which sets its recvbuf
  to 80 kB, but not ok for alternative sysloggers, like rsyslogd, which
  use the default size.

As a consequence, writing messages of more than 4 kB with syslog() as a
non-root user while running rsyslogd would cause the logging application
to spin indefinitely within syslog().

PR:		260126
MFC:		2 weeks
Sponsored by:	Axcient
Reviewed by:	markj
Differential Revision: https://reviews.freebsd.org/D33199