openvswitch: fix duplicate #include headers

The #include headers net/genetlink.h and linux/genetlink.h both were
included twice, so delete each of the duplicate.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Cc: Pravin Shelar <pshelar@nicira.com>
Cc: dev@openvswitch.org
Signed-off-by: David S. Miller <davem@davemloft.net>