socket_wrapper.c: let swrap_vioctl() handle SIOCOUTQ/TIOCOUTQ/FIONWRITE explicitly

socket_wrapper.c: let swrap_vioctl() handle SIOCOUTQ/TIOCOUTQ/FIONWRITE explicitly

They are used to ask for the number of unacked bytes in the send queue,
with AF_UNIX sockets get strange result, on linux 5.3 I get more bytes
reported than I sent into the socket. All bytes reach the destination
directly, so we can just always report 0 unacked bytes.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11897

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit f317ebcdcdd626ed9e06de2eb60031306994c803)