logd: permit app access to clear logs

I/auditd(19949): type=1400 audit(0.0:71): avc:  denied  { write } for  comm="logcat" name="logd" dev="tmpfs" ino=5924 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:logd_socket:s0 tclass=sock_file

(cherry picked from 60f0be84)

Bug: 17323719
Change-Id: Id8399195196ffad884eef98030d544c68ed0596f