net: remove [un]register_pernet_gen_... and update the docs.

No that all of the callers have been updated to set fields in
struct pernet_operations, and simplified to let the network
namespace core handle the allocation and freeing of the storage
for them, remove the surpurpflous methods and update the docs
to the new style.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netns/generic.h

@@ -12,9 +12,11 @@
  * stuff on the struct net without explicit struct net modification
  *
  * The rules are simple:
- * 1. register the ops with register_pernet_gen_device to get the id
- *    of your private pointer;
- * 2. call net_assign_generic() to put the private data on the struct
+ * 1. set pernet_operations->id.  After register_pernet_device you
+ *    will have the id of your private pointer.
+ * 2. Either set pernet_operations->size (to have the code allocate and
+ *    free a private structure pointed to from struct net ) or 
+ *    call net_assign_generic() to put the private data on the struct
  *    net (most preferably this should be done in the ->init callback
  *    of the ops registered);
  * 3. do not change this pointer while the net is alive;