Fix PR 48104

So far bridge cannot receive frames via a member interface when the frames
come from another member interface. So when we assign an IP address to
a member interface, hosts connected to another member interface cannot
ping to the IP address. That behavior isn't expected. See PR 48104 for
more realistic examples of this issue.

The change does:
- drop M_PROMISC before ether_input, which allows a bridge member interface
  to receive a frame coming from another bridge member interface
- receive broadcast/multicast frames via all bridge member interfaces,
  which is required to receive IPv6 multicast packets destined to a
  multicast group belonging to a bridge member interface that is different
  from a packet arrival interface

roy@ helped testing of the fix, thanks!

(ozaki-r)