More completely add NETLINK_NETFILTER constant.

This was added to OsConstants.java in ag/2431164. I failed to add this
required piece.  =)

Bug: 29337859

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes

Change-Id: Iae0a236b3591b3f9e102b8b335b93c458949964e
1 file changed