mac80211: Fix the Problem of Unreachable Mesh STA from DS

This patch fixes the problem of unreachable mesh STA from
Distribution System (DS) due to the introduction of previous
patch solving the mesh STA joining from one MBSS to another
MBSS.

Reported-by: Georgiewskiy Yuriy <bottleman@icf.org.ru>
Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>