Revert "sctp: do not peel off an assoc from one netns to another one"

This reverts commit 2a0e6090 which is
commit df80cd9b28b9ebaa284a41df611dbf3a2d05ca74 upstream as I messed up
by applying it to the tree twice.

Reported-by: Michal Kubecek <mkubecek@suse.cz>
Cc: ChunYu Wang <chunwang@redhat.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>