exclude Unix Domain Socket from setErrMessageCB

exclude Unix Domain Socket from setErrMessageCB

Summary:
In the latest stable kernel 4.14.3 as of 2017-12-04, unix domain socket does not support MSG_ERRQUEUE. So recvmsg(MSG_ERRQUEUE) will read application data from unix doamin socket as error message, which breaks the message flow in application. This diff disable setErrMessageCB for Unix Domain Socket.

Both [[ https://github.com/torvalds/linux/blob/master/net/ipv4/tcp.c#L1782 | tcp_recvmsg ]] and [[ https://github.com/torvalds/linux/blob/master/net/ipv4/udp.c#L1571 | udp_recvmsg ]] will check flag MSG_ERRQUEUE and read from error queue.  However, there is nothing about MSG_ERRQUEUE in [[ https://github.com/torvalds/linux/blob/master/net/unix/af_unix.c#L2249 | af_unix ]].

Reviewed By: yfeldblum

Differential Revision: D6479465

fbshipit-source-id: eba2c8650e96466f2b361a42ddf90053d65f19bd