linux-phytec-ti

gre: refactor the gre_fb_xmit

The patch refactors the gre_fb_xmit function, by creating
prepare_fb_xmit function for later ERSPAN collect_md mode patch.

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>