Address new system server denial.

Allow system_server to unlink sockets created
by the wpa supplicant. This will resolve the following
denial seen across mutliple devices.

  avc:  denied  { unlink } for  pid=584 comm="WifiStateMachin" name="wlan0" dev=mmcblk0p10 ino=138762 scontext=u:r:system_server:s0 tcontext=u:object_r:wpa_socket:s0 tclass=sock_file

Change-Id: If3a8b1f270dfcd3dc6838eb8ac72e3d5004cc36d
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>