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/phonet/af_phonet.c b/net/phonet/af_phonet.c
index 81795ea..a662e62 100644
--- a/net/phonet/af_phonet.c
+++ b/net/phonet/af_phonet.c
@@ -382,9 +382,8 @@
 	return NET_RX_DROP;
 }
 
-static struct packet_type phonet_packet_type = {
+static struct packet_type phonet_packet_type __read_mostly = {
 	.type = cpu_to_be16(ETH_P_PHONET),
-	.dev = NULL,
 	.func = phonet_rcv,
 };