bridge: use MDBA_SET_ENTRY_MAX for maxtype in nlmsg_parse()

This is just a cleanup, because in the current code MDBA_SET_ENTRY_MAX ==
MDBA_SET_ENTRY.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>