[Bluetooth] Replace info message about SCO MTU with BT_DBG

This patch replaces one BT_INFO with BT_DBG. With this change the
use of getsockopt() don't pollute the kernel log with the info about
the SCO MTU if debugging is disabled.

net/bluetooth/sco.c

@@ -698,7 +698,7 @@ int sco_sock_getsockopt(struct socket *sock, int level, int optname, char *optva
 		
 		opts.mtu = sco_pi(sk)->conn->mtu;
 
-		BT_INFO("mtu %d", opts.mtu);
+		BT_DBG("mtu %d", opts.mtu);
 
 		len = min_t(unsigned int, len, sizeof(opts));
 		if (copy_to_user(optval, (char *)&opts, len))