datapath: gre: Fix kernel 3.11 compatibility.

On 3.11 kernel, gre module exports IP_GRE demux API, ovs needs
to use it to register for GRE protocol handler.

Reported-by:  Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Tested-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Acked-by: Jesse Gross <jesse@nicira.com>
openflow-1.2.h: Fix definition of OXM_OF_PBB_ISID.

The ONF header file shows this as a 3-byte field.

Reported-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>