adapted from patch by Matthias Schiffer.

patch by Mahesh Bodapati and Jaydeep Patil of Imagination
Technologies.

....to be somewhat consistent and easily comparable with asm/socket.h
Signed-off-by: NRoman Yeryomin <roman@ubnt.com>

Signed-off-by: NRoman Yeryomin <roman@ubnt.com>

SO_REUSEPORT implementation was merged in the linux kernel commit
c617f398edd4db2b8567a28e899a88f8f574798d 2013-01-23

although a number is reserved for it, this option is not implemented
on Linux and does not work. defining it causes some applications to
use it, and subsequently break due to its failure.

why does mips have to be gratuitously incompatible in every possible
imaginable way?

the kernel wrongly expects the cmsg length field to be size_t instead
of socklen_t. in order to work around the issue, we have to impose a
length limit and copy to a local buffer. the length limit should be
more than sufficient for any real-world use; these headers are only
used for passing file descriptors and permissions between processes
over unix sockets.

basically, this version of the code was obtained by starting with
rdp's work from his ellcc source tree, adapting it to musl's build
system and coding style, auditing the bits headers for discrepencies
with kernel definitions or glibc/LSB ABI or large file issues, fixing
up incompatibility with the old binutils from aboriginal linux, and
adding some new special cases to deal with the oddities of sigaction
and pipe syscall interfaces on mips.

at present, minimal test programs work, but some interfaces are broken
or missing. threaded programs probably will not link.

this port assumes eabi calling conventions, eabi linux syscall
convention, and presence of the kernel helpers at 0xffff0f?0 needed
for threads support. otherwise it makes very few assumptions, and the
code should work even on armv4 without thumb support, as well as on
systems with thumb interworking. the bits headers declare this a
little endian system, but as far as i can tell the code should work
equally well on big endian.

some small details are probably broken; so far, testing has been
limited to qemu/aboriginal linux.

some program was undefining AF_NETLINK and thereby breaking AF_ROUTE...

after re-reading 2.2.2 of POSIX 2008, all of these are in the correct
reserved namespaces and do not need protection.

based on patch by nik

thanks to Peter Mazinger (psm) for pointing many of these issues out
and submitting a patch on which this commit is loosely based