rule: memleak in __do_add_setelems()

rule: memleak in __do_add_setelems()

This patch invokes interval_map_decompose() with named sets:

==3402== 2,352 (128 direct, 2,224 indirect) bytes in 1 blocks are definitely lost in loss record 9 of 9
==3402==    at 0x483577F: malloc (vg_replace_malloc.c:299)
==3402==    by 0x48996A8: xmalloc (utils.c:36)
==3402==    by 0x4899778: xzalloc (utils.c:65)
==3402==    by 0x487CB46: expr_alloc (expression.c:45)
==3402==    by 0x487E2A0: mapping_expr_alloc (expression.c:1140)
==3402==    by 0x4898AA8: interval_map_decompose (segtree.c:1095)
==3402==    by 0x4872BDF: __do_add_setelems (rule.c:1569)
==3402==    by 0x4872BDF: __do_add_setelems (rule.c:1559)
==3402==    by 0x4877936: do_command (rule.c:2710)
==3402==    by 0x489F1CB: nft_netlink.isra.5 (libnftables.c:42)
==3402==    by 0x489FB07: nft_run_cmd_from_filename (libnftables.c:508)
==3402==    by 0x10A9AA: main (main.c:455)

Fixes: dd44081d91ce ("segtree: Fix add and delete of element in same batch")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>