secchan: Do not refresh datapath indexes from bridge_get_ifaces().

secchan: Do not refresh datapath indexes from bridge_get_ifaces().

bridge_get_ifaces() called bridge_fetch_dp_ifaces(), which in turn would
set dp_ifidx members of struct iface to -1 if we were racing with a port
being deleted from a datapath.  When this happen it would cause
ODPAT_OUTPUT actions with the port number set to UINT16_MAX to be pushed
to the datapath on OFPP_NORMAL actions, which the datapath would choke
on with EINVAL errors.

Thanks to Justin for pointing out the bad actions being pushed to the
datapath.