Don't ever send frames on OpenFlow devices to the host stack.

Don't ever send frames on OpenFlow devices to the host stack.

On Linux 2.6 only, we would send frames received on OpenFlow devices to
the host TCP/IP stack if the dest Ethernet address matched the device's
Ethernet address (or under some other conditions).  This caused confusion
when the host stack was configured for forwarding, because received IP
packets would be forwarded to other interfaces with IP addresses even if
the device on which they were received was configured with no IP address.
(This was discovered by Murphy.  Thanks Murphy!)

This change drops this "feature".  A more or less equivalent feature that
may be less prone to confusion and which works on any kernel version will
be added in a future commit via the of%d device.

This also allowed factoring out common code from the bridge hooks.