netfilter: nf_tables: Introduce NFT_MSG_GETRULE_RESET

Analogous to NFT_MSG_GETOBJ_RESET, but for rules: Reset stateful
expressions like counters or quotas. The latter two are the only
consumers, adjust their 'dump' callbacks to respect the parameter
introduced earlier.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>