This patch adds OOB support for AF_UNIX sockets.
The semantics is same as TCP.

The last byte of a message with the OOB flag is
treated as the OOB byte. The byte is separated into
a skb and a pointer to the skb is stored in unix_sock.
The pointer is used to enforce OOB semantics.
Signed-off-by: NRao Shoaib <rao.shoaib@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>