Add some more sockmap tests to cover,

 - forwarding to NULL entries
 - more than two maps to test list ops
 - forwarding to different map
Signed-off-by: NJohn Fastabend <john.fastabend@gmail.com>
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>