Revert "ipv6: constify inet6_protocol structures"

This reverts commit 3a3a4e30.

inet6_add_protocol and inet6_del_protocol include casts that remove the
effect of the const annotation on their parameter, leading to possible
runtime crashes.
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1080,7 +1080,7 @@ static void ip6gre_fb_tunnel_init(struct net_device *dev)
 }
 
 
-static const struct inet6_protocol ip6gre_protocol = {
+static struct inet6_protocol ip6gre_protocol __read_mostly = {
 	.handler     = gre_rcv,
 	.err_handler = ip6gre_err,
 	.flags       = INET6_PROTO_NOPOLICY|INET6_PROTO_FINAL,

net/ipv6/tcp_ipv6.c

@@ -1944,7 +1944,7 @@ struct proto tcpv6_prot = {
 	.diag_destroy		= tcp_abort,
 };
 
-static const struct inet6_protocol tcpv6_protocol = {
+static struct inet6_protocol tcpv6_protocol = {
 	.early_demux	=	tcp_v6_early_demux,
 	.early_demux_handler =  tcp_v6_early_demux,
 	.handler	=	tcp_v6_rcv,

net/ipv6/udp.c

@@ -1448,7 +1448,7 @@ int compat_udpv6_getsockopt(struct sock *sk, int level, int optname,
 }
 #endif
 
-static const struct inet6_protocol udpv6_protocol = {
+static struct inet6_protocol udpv6_protocol = {
 	.early_demux	=	udp_v6_early_demux,
 	.early_demux_handler =  udp_v6_early_demux,
 	.handler	=	udpv6_rcv,