netfilter: nf_tables: replace unnecessary use of list_for_each_entry_continue()

Since there is no way for list_for_each_entry_continue() to start
interating in the middle of the list they can be replaced with a call
to list_for_each_entry().

In preparation to limit the scope of the list iterator to the list
traversal loop, the list iterator variable 'rule' should not be used
past the loop.

v1->v2:
- also replace first usage of list_for_each_entry_continue() (Florian
Westphal)

Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>