Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

NO_MAN= has been deprecated in favor of MAN= for some time, go ahead
and finish the job. ncurses is now the only Makefile in the tree that
uses it since it wasn't a simple mechanical change, and will be
addressed in a future commit.

Use '%zu' and '%zd' as appropriate for size_t / ssize_t.

Update udpzerobyte to understand that passing 0 as a length to recv(2)
will cause it to return 0, not EAGAIN.

Add UNIX domain socket support to udpzerobyte, which suggests this
regression test should be moved to the general sockets test area rather
than netinet.

Add IPv6 support to zero-size UDP transmit/receive test.

Regression test for the loopback handling of zero-length UDP packets, which
should be delivered but without payload.