bpf: add csum_diff helper to xdp as well

Useful for porting cls_bpf programs w/o increasing program
complexity limits much at the same time, so add the helper
to XDP as well.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

net/core/filter.c

@@ -3456,6 +3456,8 @@ xdp_func_proto(enum bpf_func_id func_id)
 		return &bpf_xdp_event_output_proto;
 	case BPF_FUNC_get_smp_processor_id:
 		return &bpf_get_smp_processor_id_proto;
+	case BPF_FUNC_csum_diff:
+		return &bpf_csum_diff_proto;
 	case BPF_FUNC_xdp_adjust_head:
 		return &bpf_xdp_adjust_head_proto;
 	case BPF_FUNC_xdp_adjust_meta: