menuconfig: Assign jump keys per-page instead of globally

At the moment, keys 1-9 are assigned to the first 9 search results. This patch
makes them assigned to the first 9 results per-page instead. We are much less
likely to run out of keys that way.

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Signed-off-by: Michal Marek <mmarek@suse.cz>