UPSTREAM: udp: never accept GSO_FRAGLIST packets

Currently the UDP protocol delivers GSO_FRAGLIST packets to
the sockets without the expected segmentation.

This change addresses the issue introducing and maintaining
a couple of new fields to explicitly accept SKB_GSO_UDP_L4
or GSO_FRAGLIST packets. Additionally updates  udp_unexpected_gso()
accordingly.

UDP sockets enabling UDP_GRO stil keep accept_udp_fraglist
zeroed.

v1 -> v2:
 - use 2 bits instead of a whole GSO bitmask (Willem)

Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 78352f73dc5047f3f744764cc45912498c52f3c9)
Bug: 187129171
Signed-off-by: Connor O'Brien <connoro@google.com>
Change-Id: I79d90f403c10f83f21e3f99554b6fdbfc2cc60b0