netfilter: ipset: Count non-static extension memory for userspace

Non-static (i.e. comment) extension was not counted into the memory
size. A new internal counter is introduced for this. In the case of
the hash types the sizes of the arrays are counted there as well so
that we can avoid to scan the whole set when just the header data
is requested.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>