page_pool: fix netlink dump stop/resume

If message fills up we need to stop writing. 'break' will
only get us out of the iteration over pools of a single
netdev, we need to also stop walking netdevs.

This results in either infinite dump, or missing pools,
depending on whether message full happens on the last
netdev (infinite dump) or non-last (missing pools).

Fixes: 950ab53b

 ("net: page_pool: implement GET in the netlink API")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>