restored when its removed from the bridge.
At the moment we only clear IFCAP_TXCSUM. Since a locally generated packet on
the bridge may be sent out any one or more interfaces it cant be assumed that
every card does hardware csums. Most bridges don't generate a lot of traffic
themselves so turning off offloading won't hurt, bridged packets are
unaffected.
Tested by: Bruce Walker (bmw borderware.com)
MFC after: 5 days
7c2fb83a0b