'RELENG_7_0_0_RELEASE'.

This commit was manufactured to restore the state of the 7.0-RELEASE image.

previously conditionally acquired Giant based on debug.mpsafenet.  As that
has now been removed, they are no longer required.  Removing them
significantly simplifies error-handling in the socket layer, eliminated
quite a bit of unwinding of locking in error cases.

While here clean up the now unneeded opt_net.h, which previously was used
for the NET_WITH_GIANT kernel option.  Clean up some related gotos for
consistency.

Reviewed by:	bz, csjp
Tested by:	kris
Approved by:	re (kensmith)

sendmsg() while using a 0-length msg_controllen.  This isn't allowed in
the FreeBSD system call ABI, so detect this case and set msg_control to
NULL.  This allows Linux ping to work.

Submitted by:	rdivacky

The msg variable in linux_recvmsg() was not initialized.
Copy it from userspace.

Submitted by: rdivacky

- Linux returns ENOPROTOOPT in a case of not supported opt to setsockopt.
- Return EISDIR in pread() when arg is a directory.
- Return EINVAL instead of EFAULT when namelen is not correct in accept().
- Return EINVAL instead of EACCESS if invalid access mode is entered in
  access().
- Return EINVAL instead of EADDRNOTAVAIL in a case of bad salen param
  to bind().

Submitted by:	rdivacky
Tested with:	LTP (vfork01 fails now, but it seems to be a race and
		not caused by those changes)
MFC after:	1 week

callers pass a sockaddr allocated via malloc() from M_SONAME anymore.
Instead, free it in the callers when necessary.

to populate a close_args struct and change some of the places that do.

 - unifdef __alpha__
 - revert rev. 1.66 of linux_socket.c

on their existing file descriptor references to sockets, rather than
use fgetsock() to retrieve a direct socket reference.

MFC after:	3 months

- rename some file local structure definitions, the names clash with
  autogenerated names
- on !alpha add some compatibility defines for those renamed structures
- make some functions globally visible on alpha