netfilter: ebtables: use generic table checking

Ebtables ORs (1 << NF_BR_NUMHOOKS) into the hook mask to indicate that
the extension was called from a base chain. So this also needs to be
present in the extensions' ->hooks.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>