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

Let umount build with -Wold-style-definition.

Make umount(8) WARNS=6 clean:
- Cast delimiter width to integer [1]
- Solve name conflicts against system header
- Constify parameters to avoid qualifier conflict

PR: bin/140017 [1]
Submitted by: Ulrich Spörlein <uqs spoerlein net> [1]
MFC after: 1 month
Sponsored by: iXsystems, Inc

Don't use sys/nfs/rpcv2.h - it is part of the old kernel RPC implementation
and will be removed.

Use __FBSDID over rcsid[]. Protect copyright[] where needed.

Fix a few bugs, some of which I introduced in recent commits:
- clean_mtab():
Actually use the strdup'd version of the host that we go to the
trouble of creating.
- do_umntall/do_umount:
Don't return success if clnt_create() fails.
Don't access a client pointer after it has been destroyed.
Remember to destroy the authentication information we created.

Fix some bugs and general brain damage in mounttab:
- Declare mtabhead as an extern in mounttab.h and define it only in
mounttab.c.
- Remove shared global `verbose' and instead pass it as a parameter.
- Remove the `mtabp' argument to read_mtab(). It served no purpose
whatsoever, although read_mtab() did use it as a temporary local
variable.
- Don't check for impossible conditions when parsing mounttab, and
do detect zero-length fields.
- Correctly test for strtoul() failures - just testing ERANGE is wrong.
- Include a field name in syslog errors, and avoid passing NULL to
a syslog %s field.
- Don't test if arrays are NULL.
- If there are duplicates when writing out mounttab, keep the last
entry instead of the first, as it will have a later timestamp.
- Fix a few formatting issues.

Update rpc.umntall and umount to match the mounttab interface changes.

Fixed printf format errors which corrupted /var/db/mounttab on i386's with
64-bit longs (don't assume that time_t is long; assume that time_t's are
representable as longs).

This is another in Martin Blapp's N-series of mount-related cleanups :)
Changes are:
- rpc.umntall is called at the right places now in /etc/rc*
- rpc.umntall timeout has been lowered from two days (too high) to one
- verbose messages in rpc.umntall have been clarified
- kill double entries in /var/db/mounttab when rpc.umntall is invoked
- ${early_nfs_mounts} has been removed from /etc/rc
- patched mount(8) -p to print different pass/dump values for ufs filesystems.
(last patch recieved from dan <bugg@bugg.strangled.net>)

Submitted by: Martin Blapp <mbr@imp.ch>, dan <bugg@bugg.strangled.net>

Add rpc.umntall utility, to be used by startup and shutdown scripts
to replace (broken) umntall signal code previously in mountd.

Submitted by: Martin Blapp <mb@imp.ch>