inet: remove old fragmentation hash initializing

All fragmentation hash secrets now get initialized by their
corresponding hash function with net_get_random_once. Thus we can
eliminate the initial seeding.

Also provide a comment that hash secret seeding happens at the first
call to the corresponding hashing function.

Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/inet_frag.h

@@ -64,6 +64,10 @@ struct inet_frags {
 	rwlock_t		lock ____cacheline_aligned_in_smp;
 	int			secret_interval;
 	struct timer_list	secret_timer;
+
+	/* The first call to hashfn is responsible to initialize
+	 * rnd. This is best done with net_get_random_once.
+	 */
 	u32			rnd;
 	int			qsize;
 

net/ipv4/inet_fragment.c

@@ -93,9 +93,6 @@ void inet_frags_init(struct inet_frags *f)
 	}
 	rwlock_init(&f->lock);
 
-	f->rnd = (u32) ((totalram_pages ^ (totalram_pages >> 7)) ^
-				   (jiffies ^ (jiffies >> 6)));
-
 	setup_timer(&f->secret_timer, inet_frag_secret_rebuild,
 			(unsigned long)f);
 	f->secret_timer.expires = jiffies + f->secret_interval;