nft: cache: Sort custom chains by name

nft: cache: Sort custom chains by name

With base chains no longer residing in the tables' chain lists, they can
easily be sorted upon insertion. This on one hand aligns custom chain
ordering with legacy iptables and on the other makes it predictable,
which is very helpful when manually comparing ruleset dumps for
instance.

Adjust the one ebtables-nft test case this change breaks (as wrong
ordering is expected in there). The manual output sorting done for tests
which apply to legacy as well as nft is removed in a separate patch.

Signed-off-by: Phil Sutter <phil@nwl.cc>