exposed by the security fix in FreeBSD-SA-11:05.unix.

Approved by:	so (cperciva)
Approved by:	re (kib)
Security:	Related to FreeBSD-SA-11:05.unix, but not actually
		a security fix.

Implement MSG_CMSG_CLOEXEC flag for linux_recvmsg().

Approved by:	kib (mentor)

Make linux_sendmsg() and linux_recvmsg() work on linux32/amd64.
Change types used in the linux' struct msghdr and struct cmsghdr
definitions to the properly-sized architecture-specific types.
Move ancillary data handler from linux_sendit() to linux_sendmsg().

Approved by:	kib (mentor)

Somewhere between 2.6.23 and 2.6.27, Linux added SOCK_CLOEXEC and
SOCK_NONBLOCK flags, that allow to save fcntl() calls.

Implement a variation of the socket() syscall which takes a flags
in addition to the type argument.

Approved by:	kib (mentor)

Return EINVAL in case when the incorrect or unsupported
type argument is specified.

Do not map type argument value as its Linux values are
identical to FreeBSD values.

Approved by:	kib (mentor)

Use the protocol family constants for the domain argument validation.
Return immediately when the socket() failed.

Approved by:	kib (mentor)

Emulate SO_PEERCRED socket option.
Temporarily use 0 for pid member as the FreeBSD does not cache remote
UNIX domain socket peer pid.

PR:		kern/102956
Approved by:	kib (mentor)

Return EAFNOSUPPORT instead of EINVAL in case when the incorrect or
unsupported domain argument to linux_socket() is specified.

Approved by:	kib (mentor)

Linux socketpair() call expects explicit specified protocol for
AF_LOCAL domain unlike FreeBSD which expects 0 in this case.

Return EAFNOSUPPORT in case when the incorrect domain argument
is specified.

Return EPROTONOSUPPORT instead of passing values that are not 0
to the BSD layer.

Approved by:	kib (mentor)

Validate user-supplied arguments values.
Args argument is a pointer to the structure located in user space in
which the socketcall arguments are packed. The structure must be
copied to the kernel instead of direct dereferencing.

Approved by:	kib (mentor)