Mark system_ndebug_socket as mlstrustedobject.

Address the following denial:

    audit(0.0:644): avc: denied { write } for name="ndebugsocket" dev="dm-2" ino=654091 scontext=u:r:crash_dump:s0:c512,c768 tcontext=u:object_r:system_ndebug_socket:s0 tclass=sock_file permissive=0

Bug: http://b/36278094
Test: mm
Change-Id: I0df115a3682385cee72adbfc4687221cd7c51a4d