Allow system_server to read from log daemon.

Addresses denials such as:
avc:  denied  { write } for  pid=1797 comm="logcat" name="logdr" dev="tmpfs" ino=7523 scontext=u:r:system_server:s0 tcontext=u:object_r:logdr_socket:s0 tclass=sock_file
avc:  denied  { connectto } for  pid=1797 comm="logcat" path="/dev/socket/logdr" scontext=u:r:system_server:s0 tcontext=u:r:logd:s0 tclass=unix_stream_socket

Change-Id: Idc4f48519ca3d81125102e8f15f68989500f5e9e
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>