Build mount_nfs(8) with WARNS=6.

Reviewed by:	rmacklem@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273896 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
filedesc: fix missed comments about fdsetugidsafety

While here just note that both fdsetugidsafety and fdcheckstd take sleepable
locks.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273897 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f