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>
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 96d9eda..f85ca1b 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -421,7 +421,7 @@
 
 /* ------------------------------------------------------------------------ */
 
-static struct packet_type lapbeth_packet_type = {
+static struct packet_type lapbeth_packet_type __read_mostly = {
 	.type = cpu_to_be16(ETH_P_DEC),
 	.func = lapbeth_rcv,
 };