allow ueventd sysfs_type lnk_file

ueventd is allowed to change files and directories in /sys,
but not symbolic links. This is, at a minimum, causing the
following denial:

type=1400 audit(0.0:5): avc: denied { getattr } for comm="ueventd" path="/sys/devices/tegradc.0/driver" dev=sysfs ino=3386 scontext=u:r:ueventd:s0 tcontext=u:object_r:sysfs_devices_tegradc:s0 tclass=lnk_file

Allow ueventd to modify labeling / attributes of symlinks.

Change-Id: If641a218e07ef479d1283f3171b2743f3956386d