net: convert usage of packet_type to read_mostly

Protocols that use packet_type can be __read_mostly section for better
locality. Elminate any unnecessary initializations of NULL.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/irda/irmod.c

@@ -55,7 +55,7 @@ EXPORT_SYMBOL(irda_debug);
 /* Packet type handler.
  * Tell the kernel how IrDA packets should be handled.
  */
-static struct packet_type irda_packet_type = {
+static struct packet_type irda_packet_type __read_mostly = {
 	.type	= cpu_to_be16(ETH_P_IRDA),
 	.func	= irlap_driver_rcv,	/* Packet type handler irlap_frame.c */
 };