selinux: add SOCK_DIAG_BY_FAMILY to the list of netlink message types
The SELinux AF_NETLINK/NETLINK_SOCK_DIAG socket class was missing the
SOCK_DIAG_BY_FAMILY definition which caused SELINUX_ERR messages when
the ss tool was run.

 # ss
 Netid  State  Recv-Q Send-Q  Local Address:Port   Peer Address:Port
 u_str  ESTAB  0      0                  * 14189             * 14190
 u_str  ESTAB  0      0                  * 14145             * 14144
 u_str  ESTAB  0      0                  * 14151             * 14150
 {...}
 # ausearch -m SELINUX_ERR
 ----
 time->Thu Jan 23 11:11:16 2014
 type=SYSCALL msg=audit(1390493476.445:374):
  arch=c000003e syscall=44 success=yes exit=40
  a0=3 a1=7fff03aa11f0 a2=28 a3=0 items=0 ppid=1852 pid=1895
  auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0
  tty=pts0 ses=1 comm="ss" exe="/usr/sbin/ss"
  subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null)
 type=SELINUX_ERR msg=audit(1390493476.445:374):
  SELinux:  unrecognized netlink message type=20 for sclass=32

Signed-off-by: Paul Moore <pmoore@redhat.com>