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/net/appletalk/ddp.c b/net/appletalk/ddp.c
index cf05c43..3e0671d 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1860,12 +1860,12 @@
 	.notifier_call	= ddp_device_event,
 };
 
-static struct packet_type ltalk_packet_type = {
+static struct packet_type ltalk_packet_type __read_mostly = {
 	.type		= cpu_to_be16(ETH_P_LOCALTALK),
 	.func		= ltalk_rcv,
 };
 
-static struct packet_type ppptalk_packet_type = {
+static struct packet_type ppptalk_packet_type __read_mostly = {
 	.type		= cpu_to_be16(ETH_P_PPPTALK),
 	.func		= atalk_rcv,
 };