Add a selftests that includes the following test cases:

1. Configuration tests. Both valid and invalid configurations are
   tested across all entry types (e.g., L2, IPv4).

2. Forwarding tests. Both host and port group entries are tested across
   all entry types.

3. Interaction between user installed MDB entries and IGMP / MLD control
   packets.

Example output:

INFO: # Host entries configuration tests
TEST: Common host entries configuration tests (IPv4)                [ OK ]
TEST: Common host entries configuration tests (IPv6)                [ OK ]
TEST: Common host entries configuration tests (L2)                  [ OK ]

INFO: # Port group entries configuration tests - (*, G)
TEST: Common port group entries configuration tests (IPv4 (*, G))   [ OK ]
TEST: Common port group entries configuration tests (IPv6 (*, G))   [ OK ]
TEST: IPv4 (*, G) port group entries configuration tests            [ OK ]
TEST: IPv6 (*, G) port group entries configuration tests            [ OK ]

INFO: # Port group entries configuration tests - (S, G)
TEST: Common port group entries configuration tests (IPv4 (S, G))   [ OK ]
TEST: Common port group entries configuration tests (IPv6 (S, G))   [ OK ]
TEST: IPv4 (S, G) port group entries configuration tests            [ OK ]
TEST: IPv6 (S, G) port group entries configuration tests            [ OK ]

INFO: # Port group entries configuration tests - L2
TEST: Common port group entries configuration tests (L2 (*, G))     [ OK ]
TEST: L2 (*, G) port group entries configuration tests              [ OK ]

INFO: # Forwarding tests
TEST: IPv4 host entries forwarding tests                            [ OK ]
TEST: IPv6 host entries forwarding tests                            [ OK ]
TEST: L2 host entries forwarding tests                              [ OK ]
TEST: IPv4 port group "exclude" entries forwarding tests            [ OK ]
TEST: IPv6 port group "exclude" entries forwarding tests            [ OK ]
TEST: IPv4 port group "include" entries forwarding tests            [ OK ]
TEST: IPv6 port group "include" entries forwarding tests            [ OK ]
TEST: L2 port entries forwarding tests                              [ OK ]

INFO: # Control packets tests
TEST: IGMPv3 MODE_IS_INCLUE tests                                   [ OK ]
TEST: MLDv2 MODE_IS_INCLUDE tests                                   [ OK ]
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>