af_packet: tone down the Tx-ring unsupported spew.

[Dave Jones]

Trinity and other fuzzers can hit this WARN on far too easily,
resulting in a tainted kernel that hinders automated fuzzing.

Replace it with a rate-limited printk.

Signed-off-by: Dave Jones <da...@codemonkey.org.uk>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 1ecfa710ca98..f12c17f355d9 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4151,7 +4151,7 @@ static int packet_set_ring(struct sock *sk, union 
tpacket_req_u *req_u,
 
        /* Opening a Tx-ring is NOT supported in TPACKET_V3 */
        if (!closing && tx_ring && (po->tp_version > TPACKET_V2)) {
-               WARN(1, "Tx-ring is not supported.\n");
+               net_warn_ratelimited("Tx-ring is not supported.\n");
                goto out;
        }