rework).  MFC r237563, r239511, r243603, r245915, r245916, r245919,
r245921, r245922, r245924, r245925, r245932, r245934 too.

Build tested with make universe.

r237263:
- Updated TOE support in the kernel.
...

r237563:
Fix clang warning when compiling iw_cxgb.

r239511:
Correctly handle the case where an inp has already been dropped by the time
the TOE driver reports that an active open failed.  toe_connect_failed is
supposed to handle this but it should be provided the inpcb instead of the
tcpcb which may no longer be around.

r243603:
Make sure that tcp_timer_activate() correctly sees TCP_OFFLOAD (or not).

r245915:
Heed SO_NO_OFFLOAD.

r245916:
Teach toe_4tuple_check() to deal with IPv6 4-tuples too.

r245919:
Add TCP_OFFLOAD hook in syncache_respond for IPv6 too, just like the one
that exists for IPv4.

r245921:
There is no need to call into the TOE driver twice in pru_rcvd (tod_rcvd
and then tod_output right after that).

r245922:
Avoid NULL dereference in nd6_storelladdr when no mbuf is provided.  It
is called this way from a couple of places in the OFED code.  (toecore
calls it too but that's going to change shortly).

r245924:
Move lle_event to if_llatbl.h

lle_event replaced arp_update_event after the ARP rewrite and ended up
in if_ether.h simply because arp_update_event used to be there too.
IPv6 neighbor discovery is going to grow lle_event support and this is a
good time to move it to if_llatbl.h.

The two in-tree consumers of this event - OFED and toecore - are not
affected.

r245925:
Generate lle_event in the IPv6 neighbor discovery code too.

r245932:
Teach toe_l2_resolve to resolve IPv6 destinations too.

r245934:
Add checks for SO_NO_OFFLOAD in a couple of places that I missed earlier
in r245915.

  Use IP6STAT_INC/IP6STAT_DEC macros to update ip6 stats.

MFC r249528,249546:
  Add accounting to the source address selection algorithm for cases, when
  it fails to select an address, also add several another counters to
  the statistics.

MFC r249543,249552:
  Replace hardcoded numbers.

MFC r249544:
  Use IP6S_M2MMAX macro.

MFC r249545:
  Replace hardcoded numbers. Also use interface-local scope name instead
  of node-local.

Document netstat -Q flags meaning.

Show how many times we are blocked waiting for mbufs.

	Remove unused variable. Newer versions of gcc care.

Approved by:	cperciva (implicit)

Teach netstat(1) -z to reset these sysctls.

Changes which improve compilation if neither INET nor INET6 is defined.

Allow netstat to be build if INET is not defined in the kernel.
Thanks to Garrett Cooper for reporting the issue.

This also fixes a bug where netstat doesn't work correctly for SCTP
on INET only (no INET6) kernels.

Approved by: re@

Eliminate an unused parameter of static method igmp_stats_live_old().

After r232745, which makes sure __bswap16(), ntohs() and htons() return
__uint16_t, we can partially undo r228668.

Note the remark "Work around a clang false positive with format string
warnings and ntohs macros (see LLVM PR 11313)" was actually incorrect.

Before r232745, on some arches, the ntohs() macros did in fact return
int, not uint16_t, so clang was right in warning about the %hu format
string.

Define several extra macros in bsd.sys.mk and sys/conf/kern.pre.mk, to
get rid of testing explicitly for clang (using ${CC:T:Mclang}) in
individual Makefiles.

Instead, use the following extra macros, for use with clang:
- NO_WERROR.clang       (disables -Werror)
- NO_WCAST_ALIGN.clang  (disables -Wcast-align)
- NO_WFORMAT.clang	(disables -Wformat and friends)
- CLANG_NO_IAS		(disables integrated assembler)
- CLANG_OPT_SMALL	(adds flags for extra small size optimizations)

As a side effect, this enables setting CC/CXX/CPP in src.conf instead of
make.conf!  For clang, use the following:

CC=clang
CXX=clang++
CPP=clang-cpp