MFC r244236,r244408,r244915,r247054,r251512:

  Add a new knob WITH_DEBUG_FILES to control the building of standalone
  debug files for userland programs and libraries.  The "-g" debug flag
  is automatically applied when WITH_DEBUG_FILES is set.

  The debug files are named ${prog}.debug and ${shlib}.debug for                  consistency with other systems and documentation.  In addition they are
  installed under /usr/lib/debug, to simplify the process of installing
  them if needed after a crash.  Users of bsd.{prog,lib}.mk outside of the
  base system place the standalone debug files in a .debug subdirectory.
  GDB automatically searches both of these directories for standalone
  debug files.
MFC r243624:

  Remove unused and unnecessary CSUM_IP_FRAGS checksumming capability.
  Checksumming the IP header of fragments is no different from doing
  normal IP headers.

  Discussed with:	yongari

Note that the definition of CSUM_IP_FRAGS is left in mbuf.h to allow
for stable branch source compatibility.
MFC r252313, r252349, 252436:

To avoid LOR, drop the filedesc lock in export_fd_to_sb(), before
writing to sbuf.

MFC r252351 (mjg):

Remove duplicate NULL check in kern_proc_filedesc_out.
No functional changes.
Undo accidental MFC of GPL_DTC in r252827
MFC r241724:

  Remove splimp() comment from sysinit table and attribute SI_SUB_PROTO_BEGIN
  and SI_SUB_PROTO_END to VNET related initializations.
Regenerate after r252827
MFC r226433:

 Update the comment and description of tcp_sendspace and tcp_recvspace
 to better reflect their purpose.

MFC r226437:

 VNET virtualize tcp_sendspace/tcp_recvspace and change the
 type to INT.  A long is not necessary as the TCP window is
 limited to 2**30.  A larger initial window isn't useful.

MFC r226448:

 Move the tcp_sendspace and tcp_recvspace sysctl's from
 the middle of tcp_usrreq.c to the top of tcp_output.c
 and tcp_input.c respectively next to the socket buffer
 autosizing controls.

MFC r227034:

 Restore sysctl names for tcp_sendspace/tcp_recvspace.

 They seem to be changed unintentionally in r226437, and there were no
 any mentions of renaming in commit log message.

 Reported by:	Anton Yuzhaninov <citrin citrin ru>