tftpd: Satisfy clang-analyzer.

* Replace `random()` with `arc4random()`.
* Change some variable types.
* Drop some unused assignments.

MFC after: 3 days
Sponsored by: Klara, Inc.
Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D45132

libexec: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

tftpd: Use poll() instead of alarm() + setjmp().

While there, don't log an error when timing out waiting for a possible retransmit after a successful transfer.

Sponsored by: Klara, Inc.
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D38966

tftpd: Plug memory leaks in option handling code.

Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D37423

tftpd: whitespace cleanup

tftpd: cleanup

Sponsored by: Klara, Inc.

When dropping packets (RRQ or WRQ) for debugging, report the send
operation as successful. Reporting a failure stops the transfer
instead of using timeouts.

MFC after: 1 week

Fix several Coverity warnings in tftp

Some of the changes are in the libexec/tftpd directory, but to functions that
are only used by tftp(1) (they share some code).

* strcpy => strlcpy (1006793, 1006794, 1006796, 1006741)
* Unchecked return value and TOCTTOU (1009314)
* NULL pointer dereference (1018035, 1018036)

Reported by: Coverity
CID: 1006793, 1006794, 1006796, 1006741, 1009314, 1018035
CID: 1018036
MFC after: 2 weeks

Fix multiple Coverity warnings in tftpd(8)

* Initialize uninitialized variable (CID 1006502)
* strcpy => strlcpy (CID 1006792, 1006791, 1006790)
* Check function return values (CID 1009442, 1009441, 1009440)
* Delete dead code in receive_packet (not reported by Coverity)
* Remove redundant alarm(3) in receive_packet (not reported by Coverity)

Reported by: Coverity
CID: 1006502, 1006792, 1006791, 1006790, 1009442, 1009441, 1009440
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D11287

libexec: 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.

Mark tftp_log() as __printflike() (which would have caught the bug
fixed in r246106) and deal with the fallout.

MFC after: 2 weeks

Remove extra %s from debug statement that ends up crashing tftpd if
debug is set very high (like -d15 in my case).

Obtained from: Yahoo! Inc
MFC after: 2 weeks

Use correct size in snprintf.
Remove unused buffer.

PR: 174631
Submitted by: Henning Petersen
MFC after: 1 month

Fix warnings found by -Wmising-variable-declarations.

This self-written compiler warning, which is hopefully going to be
committed into LLVM sources soon, warns about potentially missing
`static' keywords, similar to -Wmissing-prototypes.

- bin/pax: Move external declaration of chdname and s_mask into extern.h.
- bin/setfacl: Move setfacl.c-specific stuff out of setfacl.h.
- sbin/mount_fusefs: Remove char *progname; use getprogname().
- others: add `static' where possible.

Avoid error log for transfer stop w/o error code.

A number of tftp clients, including the one in Intel's pxe boot loader,
may intentionally stop a transfer using error code 0 (i.e., EUNDEF).
These are not real errors. Avoid spamming log files with these by
logging them at level LOG_DEBUG instead.

Discussed on -hackers with an initial patch proposal; this change is an
improved approach suggested by kan@.

Fix warning when compiling with gcc46:
error: variable 'bp' set but not use

Approved by: dim
MFC After: 3 days

Spelling fixes for libexec/

Fix tftp_log() usage.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Move the pfrom initialization from before the setjmp to after the
setjmp to avoid warnings on the powerpc build...

Bring in new files from edwin's tftp