Newer adbd versions use functionfs instead of a custom adb usb gadget.
Make sure the functionfs filesystem is properly labeled, and that adbd
has access to the functionfs files.

Once labeled, this addresses the following denials:

<12>[   16.127191] type=1400 audit(949060866.189:4): avc:  denied  { read write } for  pid=223 comm="adbd" name="ep0" dev="functionfs" ino=5489 scontext=u:r:adbd:s0 tcontext=u:object_r:functionfs:s0 tclass=file
<12>[   16.127406] type=1400 audit(949060866.189:5): avc:  denied  { open } for  pid=223 comm="adbd" path="/dev/usb-ffs/adb/ep0" dev="functionfs" ino=5489 scontext=u:r:adbd:s0 tcontext=u:object_r:functionfs:s0 tclass=file
<12>[  377.366011] type=1400 audit(949061227.419:16): avc:  denied  { ioctl } for  pid=225 comm="adbd" path="/dev/usb-ffs/adb/ep2" dev="functionfs" ino=5564 scontext=u:r:adbd:s0 tcontext=u:object_r:functionfs:s0 tclass=file

Change-Id: Iee8b522e48b4d677fd12f7c83dbc7ffbc9543ad2