batman-adv: Return EINVAL on invalid gw_bandwidth change
batman-adv: Return EINVAL on invalid gw_bandwidth change

Invalid speed settings by the user are currently acknowledged as correct
but not stored. Instead the return of the store operation of the file
"gw_bandwidth" should indicate that the given value is not acceptable.

Signed-off-by: Sven Eckelmann <dd860110a62b19214c4ee03aec0abffecb4e86b8@narfation.org>
Signed-off-by: Marek Lindner <5760fd64db566c47bfb7ce809fea1d3e512880cf@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a08f08bac39aeae6c9580ade7aa8387b5a0e7428@meshcoding.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs