MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

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

Remove UFS-specific parts from mount(8).
For mounting UFS, all mount options are passed directly to nmount(),
without any UFS-specific logic.

- Minor fixes to raise WARNS level to 6.
- Teach the mount program to call the nmount() syscall directly
- Preserve existing method of calling mount() for UFS, until we clean things
up.
- Preserve existing method of forking and calling external mount programs for
mfs, msdosfs, nfs, nfs4, ntfs, nwfs, nullfs, portalfs, reiserfs, smbfs,
udf, umapfs, unionfs
- devfs, linprocfs, procfs, ext2fs call nmount() syscall directly, since
that is all those external mount programs were doing

Reviewed by: phk
Discussed on: arch

Switch from K&R-style C prototypes to ISO/ANSI-style C prototypes.
Make prototype in extern.h match prototype in mount_ufs.c

o __P removed
o main prototype removed

$Id$ -> $FreeBSD$

Moved getmntops() stuff back to mntopt.h so that it is visible in other
mount utilities.

Forgot to cvs add this new file.