sockets: garbage collect SS_ISCONFIRMING

Fixes: 8df32b19dee92b5eaa4b488ae78dca6accfcb38e

sockets: don't malloc/free sockaddr memory on getpeername/getsockname

Just like it was done for accept(2) in cfb1e92912b4, use same approach
for two simplier syscalls that return socket addresses. Although,
these two syscalls aren't performance critical, this change generalizes
some code between 3 syscalls trimming code size.

Following example of accept(2), provide VNET-aware and INVARIANT-checking
wrappers sopeeraddr() and sosockaddr() around protosw methods.

Reviewed by: tuexen
Differential Revision: https://reviews.freebsd.org/D42694

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

protosw: refactor protosw and domain static declaration and load

o Assert that every protosw has pr_attach. Now this structure is
only for socket protocols declarations and nothing else.
o Merge struct pr_usrreqs into struct protosw. This was suggested
in 1996 by wollman@ (see 7b187005d18ef), and later reiterated
in 2006 by rwatson@ (see 6fbb9cf860dcd).
o Make struct domain hold a variable sized array of protosw pointers.
For most protocols these pointers are initialized statically.
Those domains that may have loadable protocols have spacers. IPv4
and IPv6 have 8 spacers each (andre@ dff3237ee54ea).
o For inetsw and inet6sw leave a comment noting that many protosw
entries very likely are dead code.
o Refactor pf_proto_[un]register() into protosw_[un]register().
o Isolate pr_*_notsupp() methods into uipc_domain.c

Reviewed by: melifaro
Differential revision: https://reviews.freebsd.org/D36232

LinuxKPI: Constantly use _LINUXKPI_ prefix in include guards

MFC after: 1 week
Reviewed by: bz, emaste, hselasky, manu
Differential Revision: https://reviews.freebsd.org/D33562

LinuxKPI: add net_ratelimit()

Add a net_ratelimit() compat implementation based on ppsratecheck().
Add a sysctl to allow tuning of the number of messages.

Sponsored-by: The FreeBSD Foundation
MFC-after: 2 weeks
Reviewed-by: hselasky
Differential Revision: https://reviews.freebsd.org/D29399

Make all the LinuxKPI include files compile standalone.

Sponsored by: Mellanox Technologies

Finish process of moving the LinuxKPI module into the default kernel build.

- Move all files related to the LinuxKPI into sys/compat/linuxkpi and
its subfolders.
- Update sys/conf/files and some Makefiles to use new file locations.
- Added description of COMPAT_LINUXKPI to sys/conf/NOTES which in turn
adds the LinuxKPI to all LINT builds.
- The LinuxKPI can be added to the kernel by setting the
COMPAT_LINUXKPI option. The OFED kernel option no longer builds the
LinuxKPI into the kernel. This was done to keep the build rules for
the LinuxKPI in sys/conf/files simple.
- Extend the LinuxKPI module to include support for USB by moving the
Linux USB compat from usb.ko to linuxkpi.ko.
- Bump the FreeBSD_version.
- A universe kernel build has been done.

Reviewed by: np @ (cxgb and cxgbe related changes only)
Sponsored by: Mellanox Technologies