netlink: monitor: fix how rules with intervals are printed

netlink: monitor: fix how rules with intervals are printed

Previous to this patch, if we add a rule like this:
 nft add rule filter test ip saddr { 1.1.1.1-2.2.2.2 }

The monitor operation output shows:
 add rule ip filter test ip saddr { 0.0.0.0, 1.1.1.1, 2.2.2.3}

The fix suggested by Pablo is to call interval_map_decompose().

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>