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/8021q/vlan.c b/net/8021q/vlan.c
index 4163ea6..2b7390e 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -51,7 +51,7 @@
 static const char vlan_copyright[] = "Ben Greear <greearb@candelatech.com>";
 static const char vlan_buggyright[] = "David S. Miller <davem@redhat.com>";
 
-static struct packet_type vlan_packet_type = {
+static struct packet_type vlan_packet_type __read_mostly = {
 	.type = cpu_to_be16(ETH_P_8021Q),
 	.func = vlan_skb_recv, /* VLAN receive method */
 };