datapath: Properly set L4 keys on "later" IP fragments

datapath: Properly set L4 keys on "later" IP fragments

Upstream commit:
    commit ad06a566e118e57b852cab5933dbbbaebb141de3
    Author: Greg Rose <gvrose8192@gmail.com>
    Date:   Tue Aug 27 07:58:09 2019 -0700

    openvswitch: Properly set L4 keys on "later" IP fragments

    When IP fragments are reassembled before being sent to conntrack, the
    key from the last fragment is used.  Unless there are reordering
    issues, the last fragment received will not contain the L4 ports, so the
    key for the reassembled datagram won't contain them.  This patch updates
    the key once we have a reassembled datagram.

    The handle_fragments() function works on L3 headers so we pull the L3/L4
    flow key update code from key_extract into a new function
    'key_extract_l3l4'.  Then we add a another new function
    ovs_flow_key_update_l3l4() and export it so that it is accessible by
    handle_fragments() for conntrack packet reassembly.

    Co-authored-by: Justin Pettit <jpettit@ovn.org>
    Signed-off-by: Greg Rose <gvrose8192@gmail.com>
    Acked-by: Pravin B Shelar <pshelar@ovn.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Justin Pettit <jpettit@ovn.org>