vswitch: Fix handling of ARPs received on bonded interfaces.

vswitch: Fix handling of ARPs received on bonded interfaces.

The vswitch must handle ARPs directed to broadcast that arrived on bonded
interfaces differently based on whether they are ARP requests or replies.
This cannot be done in a flow-based manner using OpenFlow, because
OpenFlow does not distinguish between ARP requests and replies.  Thus,
every such packet must be handled separately by the bonding code, and a
flow must not be set up.

Before secchan was integrated into vswitch, this was handled correctly.
This commit restores that correct behavior, by making it possible for
a normal-action callback to signal that the actions must not be used to
set up a flow.