This data structure holds an array of allocated strings for use in
nftnl_chain and nftnl_flowtable structs. For convenience, implement
functions to clear, populate and iterate over contents.
While at it, extend chain and flowtable tests to cover these attributes,
too.
Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>
