bridge: Fix enforcement of multicast hash_max limit

The hash size is doubled when it needs to grow and compared against
hash_max. The >= comparison will limit the hash table size to half
of what is expected i.e. the default 512 hash_max will not allow
the hash table to grow larger than 256.

Also print the hash table limit instead of the desirable size when
the limit is reached.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>