OpenVSwitch patch update

After a few discussions with the guys working on OpenVSwitch
they've recommended we use the EXTRA_CFLAGS env var for setting
flags for the kernel module.

They've updated the trunk with a patch to accommodate that.
That patch is also in this pull request and replaces a patch that I proposed.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>