As the netfilter folks don't seem to have any interest in 2.5 currently
I decided to fix their last uses of those old module interfaces myself.
The implementation (get a reference first and release it again when
not actually needed) might be slightly suboptimial but the netfilter
team should just fix it if/when they get any interest in Linux 2.5/2.6.

Also fix the MOD_INC_USE_COUNT/MOD_DEC_USE_COUNT to give more accurate
deprecation warnings.