tests: Introduce test for set with concatenated ranges

tests: Introduce test for set with concatenated ranges

This test checks that set elements can be added, deleted, that
addition and deletion are refused when appropriate, that entries
time out properly, and that they can be fetched by matching values
in the given ranges.

v5:
 - speed this up by performing the timeout test for one single
   permutation (Phil Sutter), by decreasing the number of
   permutations from 96 to 12 if this is invoked by run-tests.sh
   (Pablo Neira Ayuso) and by combining some commands into single
   nft calls where possible: with dash 0.5.8 on AMD Epyc 7351 the
   test now takes 1.8s instead of 82.5s
 - renumber test to 0043, 0042 was added meanwhile
v4: No changes
v3:
 - renumber test to 0042, 0041 was added meanwhile
v2:
 - actually check an IPv6 prefix, instead of specifying everything
   as explicit ranges in ELEMS_ipv6_addr
 - renumber test to 0041, 0038 already exists

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Acked-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>