Define MEMIF_SOCKET_UN_SIZE to size of unix domain socket address.
Report error in case of longer path.
Fixes: b923866c6974 ("net/memif: allow for full key size in socket name")
Signed-off-by: Jakub Grajciar <jgrajcia@cisco.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>