src: restore --echo with anonymous sets

src: restore --echo with anonymous sets

If --echo is passed, then the cache already contains the commands that
have been sent to the kernel. However, anonymous sets are an exception
since the cache needs to be updated in this case.

Remove the old cache logic from the monitor code that has been replaced
by 01e5c6f0ed03 ("src: add cache level flags").

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