MFC: r317931
Fix mount_nfs so that it doesn't create mounttab entries for NFSv4 mounts.

The NFSv4 protocol doesn't use the Mount protocol, so it doesn't make sense
to add an entry for an NFSv4 mount to /var/db/mounttab. Also, r308871
modified umount so that it doesn't remove any entry created by mount_nfs.

MFC: r285260
Since the case where secflavor < 0 indicates the security flavor is
to be negotiated, it could be a Kerberized mount. As such, filling
in the "principal" argument using the canonized host name makes sense.
If it is negotiated as AUTH_SYS, the "principal" argument is meaningless
but harmless.

MFC r273896:

Build mount_nfs(8) with WARNS=6.

Sponsored by: The FreeBSD Foundation

MFC r273848:

Get rid of obsolete code in mount_nfs(8).

MFC r273861:

Remove two functions unused after r273848. Would be nice if clang
or at least scan-build yelled about it.

Sponsored by: The FreeBSD Foundation

MFC r273849:

Add support for "timeo", "actimeo", "noac", and "proto" options
to mount_nfs(8). They are implemented on Linux, OS X, and Solaris,
and thus can be expected to appear in automounter maps.

Sponsored by: The FreeBSD Foundation

MFC r269583:

Provide -o vers= support for mount_nfs.

Our mount_nfs does use -o nfsv<2|3|4> or -2 or -3 to specify the version.
OSX (these days), Solaris, and Linux use -o vers=<2,3,4>.

With the upcoming autofs support we can make a lot of (entrerprisy) setups
getting mount options from LDAP just work by providing -o vers= compatibility.

Reviewed by: wblock, bjk (man page), rmacklem, emaste
Sponsored by: DARPA,AFRL
PR: 192379

MFC: r285260
Since the case where secflavor < 0 indicates the security flavor is
to be negotiated, it could be a Kerberized mount. As such, filling
in the "principal" argument using the canonized host name makes sense.
If it is negotiated as AUTH_SYS, the "principal" argument is meaningless
but harmless.

MFC r273896:

Build mount_nfs(8) with WARNS=6.

Sponsored by: The FreeBSD Foundation

MFC r273848:

Get rid of obsolete code in mount_nfs(8).

MFC r273861:

Remove two functions unused after r273848. Would be nice if clang
or at least scan-build yelled about it.

Sponsored by: The FreeBSD Foundation

MFC r273849:

Add support for "timeo", "actimeo", "noac", and "proto" options
to mount_nfs(8). They are implemented on Linux, OS X, and Solaris,
and thus can be expected to appear in automounter maps.

Sponsored by: The FreeBSD Foundation

MFC r269583:

Provide -o vers= support for mount_nfs.

Our mount_nfs does use -o nfsv<2|3|4> or -2 or -3 to specify the version.
OSX (these days), Solaris, and Linux use -o vers=<2,3,4>.

With the upcoming autofs support we can make a lot of (entrerprisy) setups
getting mount options from LDAP just work by providing -o vers= compatibility.

Reviewed by: wblock, bjk (man page), rmacklem, emaste
Sponsored by: DARPA,AFRL
PR: 192379