udp: move udp->accept_udp_{l4|fraglist} to udp->udp_flags

[ Upstream commit f5f52f08 ]

These are read locklessly, move them to udp_flags to fix data-races.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Stable-dep-of: 70a36f57 ("udp: annotate data-races around udp->encap_type")
Signed-off-by: Sasha Levin <sashal@kernel.org>