[AF_KEY]: Fix oops by converting to proc_net_*().

To make sure the procfs visibility occurs after the ->proc_fs ops are
setup, use proc_net_fops_create() and proc_net_remove().

This also fixes an OOPS after module unload in that the name string
for remove was wrong, so it wouldn't actually be removed.  That bug
was introduced by commit 61145aa1


("[KEY]: Clean up proc files creation a bit.")

Signed-off-by: David S. Miller <davem@davemloft.net>