Fix 2.13 libapparmor so version
ab0f4ab2 increased AA_LIB_REVISION and
AA_LIB_AGE, with the result that 2.13.5 builds libapparmor.so.0.7.3,
while 2.13.4 had libapparmor-1.6.2
This patch reverts the AA_LIB_AGE increase to fix the so name so that
we'll get libapparmor-1.6.3.
Note: If you want to apply this fix on top of the 2.13.5 tarball, you'll
need to also apply the patch to Makefile.in.