datapath: Add support for kernel 3.14.

Signed-off-by: Pritesh Kothari <pritesh.kothari@cisco.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
datapath: clear l4_rxhash in skb_clear_hash.

Signed-off-by: Pritesh Kothari <pritesh.kothari@cisco.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>