nconfig: minor fix

This patch fixes two problems reported by Jan Engelhardt:
1) Border is now properly placed, to always be visible
2) Long menu items are properly displayed

Reported-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Nir Tzachar <nir.tzachar@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>