bonding: Fix unnecessary warnings and logs from bond_xdp_get_xmit_slave()

syzbot reported a WARNING in bond_xdp_get_xmit_slave. To reproduce
this[1], one bond device (bond1) has xdpdrv, which increases
bpf_master_redirect_enabled_key. Another bond device (bond0) which is
unsupported by XDP but its slave (veth3) has xdpgeneric that returns
XDP_TX. This triggers WARN_ON_ONCE() from the xdp_master_redirect().
To reduce unnecessary warnings and improve log management, we need to
delete the WARN_ON_ONCE() and add ratelimit to the netdev_err().

[1] Steps to reproduce:
    # Needs tx_xdp with return XDP_TX;
    ip l add veth0 type veth peer veth1
    ip l add veth3 type veth peer veth4
    ip l add bond0 type bond mode 6 # BOND_MODE_ALB, unsupported by XDP
    ip l add bond1 type bond # BOND_MODE_ROUNDROBIN by default
    ip l set veth0 master bond1
    ip l set bond1 up
    # Increases bpf_master_redirect_enabled_key
    ip l set dev bond1 xdpdrv object tx_xdp.o section xdp_tx
    ip l set veth3 master bond0
    ip l set bond0 up
    ip l set veth4 up
    # Triggers WARN_ON_ONCE() from the xdp_master_redirect()
    ip l set veth3 xdpgeneric object tx_xdp.o section xdp_tx

Reported-by: syzbot+c187823a52ed505b2257@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c187823a52ed505b2257
Fixes: 9e2ee5c7 ("net, bonding: Add XDP support to the bonding driver")
Signed-off-by: Jiwon Kim <jiwonaid0@gmail.com>
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20240918140602.18644-1-jiwonaid0@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/bonding/bond_main.c

@@ -5610,9 +5610,9 @@ bond_xdp_get_xmit_slave(struct net_device *bond_dev, struct xdp_buff *xdp)
 		break;
 
 	default:
-		/* Should never happen. Mode guarded by bond_xdp_check() */
-		netdev_err(bond_dev, "Unknown bonding mode %d for xdp xmit\n", BOND_MODE(bond));
-		WARN_ON_ONCE(1);
+		if (net_ratelimit())
+			netdev_err(bond_dev, "Unknown bonding mode %d for xdp xmit\n",
+				   BOND_MODE(bond));
 		return NULL;
 	}