Added option for old firmware version (10.1 API v2). It seems that recent
firmware versions are constantly crashing (at least on a QCA9880-BR4A-R) and
this provides the option to select an older version instead.

Backport of r46340
Signed-off-by: Günther Kelleter <guenther.kelleter@devolo.de>

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46443 3c298f89-4303-0410-b956-a3cf2f4a3e73