In order to allow handlers directly read upcalls from datapath,
we need to support per-handler netlink socket for each vport in
datapath.  This commit makes this happen.  Also, it is guaranteed
to be backward compatible with previous branch.
Signed-off-by: NAlex Wang <alexw@nicira.com>
Acked-by: NThomas Graf <tgraf@redhat.com>
Signed-off-by: NPravin B Shelar <pshelar@nicira.com>