ofproto-dpif: Check for EBUSY as well

ofproto-dpif: Check for EBUSY as well

Guru reported that we can't create more than one geneve tunnel.
Sometimes a driver will return EBUSY as well as EEXIST for some
duplicate configurations.  Check for EBUSY too.

Fixes: 7521e0cf9e ("ofproto-dpif: Let the dpif report when a ...")
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2018-August/047214.html
Reported-by: Guru Shetty <guru@ovn.org>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>