netns: constify net_hash_mix() and various callers

const qualifiers ease code review by making clear
which objects are not written in a function.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 5105759..375dc71 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -107,7 +107,7 @@
 
 static struct hlist_head inet_addr_lst[IN4_ADDR_HSIZE];
 
-static u32 inet_addr_hash(struct net *net, __be32 addr)
+static u32 inet_addr_hash(const struct net *net, __be32 addr)
 {
 	u32 val = (__force u32) addr ^ net_hash_mix(net);