mac802154: Increase tx_buffer_len

Increase the buffer length from 10 to 300 packets. Consider that traffic on
mac802154 devices will often be 6LoWPAN, and a full-length (1280 octet)
IPv6 packet will fragment into 15 6LoWPAN fragments (because the MTU of
IEEE 802.15.4 is 127).  A 300-packet queue is really 20 full-length IPv6
packets.

With a queue length of 10, an entire IPv6 packet was unable to get queued
at one time, causing fragments to be dropped, and making reassembly
impossible.
Signed-off-by: Alan Ott <alan@signal11.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mac802154/wpan.c

@@ -360,7 +360,7 @@ void mac802154_wpan_setup(struct net_device *dev)
 	dev->header_ops		= &mac802154_header_ops;
 	dev->needed_tailroom	= 2; /* FCS */
 	dev->mtu		= IEEE802154_MTU;
-	dev->tx_queue_len	= 10;
+	dev->tx_queue_len	= 300;
 	dev->type		= ARPHRD_IEEE802154;
 	dev->flags		= IFF_NOARP | IFF_BROADCAST;
 	dev->watchdog_timeo	= 0;