datapath: Backport: vxlan: interpret IP headers for ECN correctly

datapath: Backport: vxlan: interpret IP headers for ECN correctly

Upstream commit:
    When looking for outer IP header, use the actual socket address family, not
    the address family of the default destination which is not set for metadata
    based interfaces (and doesn't have to match the address family of the
    received packet even if it was set).

    Fix also the misleading comment.

    Signed-off-by: Jiri Benc <jbenc@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream: ce212d0f6f5 ("vxlan: interpret IP headers for ECN correctly")
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Jesse Gross <jesse@kernel.org>