evaluate: Update cache on flush ruleset

evaluate: Update cache on flush ruleset

After a flush, the cache should be empty, otherwise the cache and the expected
state are desynced, causing unwarranted errors. See
tests/shell/testcases/cache/0002_interval_0.

`flush table` and `flush chain` don't empty sets or destroy chains, so the cache
does not need an update in those cases, since only chain names and set contents
are held in cache for commands other than "list"

Reported-by: Leon Merten Lohse <leon@green-side.de>
Signed-off-by: Anatole Denis <anatole@rezel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>