datapath: Account for now exposed VXLAN definitions

datapath: Account for now exposed VXLAN definitions

This brings the compat version of vxlan_udp_encap_recv() and
vxlan_xmit_skb() in line with upstream commit:

	commit 3bf3947526c1053ddf2523f261395d682718f56c
	Author: Tom Herbert <therbert@google.com>
	Date:   Thu Jan 8 12:31:18 2015 -0800

    vxlan: Improve support for header flags

    This patch cleans up the header flags of VXLAN in anticipation of
    defining some new ones:

    - Move header related definitions from vxlan.c to vxlan.h
    - Change VXLAN_FLAGS to be VXLAN_HF_VNI (only currently defined flag)
    - Move check for unknown flags to after we find vxlan_sock, this
      assumes that some flags may be processed based on tunnel
      configuration
    - Add a comment about why the stack treating unknown set flags as an
      error instead of ignoring them

    Signed-off-by: Tom Herbert <therbert@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream: 3bf394 ("vxlan: Improve support for header flags")
Signed-off-by: Thomas Graf <tgraf@noironetworks.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>