libbpf: Only check mode flags in get_xdp_id

The commit in the Fixes tag changed get_xdp_id to only return prog_id
if flags is 0, but there are other XDP flags than the modes - e.g.,
XDP_FLAGS_UPDATE_IF_NOEXIST. Since the intention was only to look at
MODE flags, clear other ones before checking if flags is 0.

Fixes: f07cbad2 ("libbpf: Fix bpf_get_link_xdp_id flags handling")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrey Ignatov <rdna@fb.com>

tools/lib/bpf/netlink.c

@@ -321,6 +321,8 @@ int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
 
 static __u32 get_xdp_id(struct xdp_link_info *info, __u32 flags)
 {
+	flags &= XDP_FLAGS_MODES;
+
 	if (info->attach_mode != XDP_ATTACHED_MULTI && !flags)
 		return info->prog_id;
 	if (flags & XDP_FLAGS_DRV_MODE)