openvswitch: remove unnecessary EXPORT_SYMBOLs

Some symbols exported to other modules are really used only by
openvswitch.ko. Remove the exports.

Tested by loading all 4 openvswitch modules, nothing breaks.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>