netfilter: nfnetlink: skip error delivery on batch in case of ENOMEM

If caller reports ENOMEM, then stop iterating over the batch and send a
single netlink message to userspace to report OOM.

Fixes: cbb8125e

 ("netfilter: nfnetlink: deliver netlink errors on batch completion")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>