FST: Fix search for peer's "other" connection

FST: Fix search for peer's "other" connection

Upon receiving FST Setup Request from some peer on some interface,
search is made to see if same peer is connected on other interface with
specific band_id. With multiple peers, bug in
fst_group_does_iface_appear_in_other_mbies() caused wrong peer address
to be returned sometimes.

Fix this with a modified, simplified search algorithm of peer's "other"
connection.

Signed-off-by: Dedy Lansky <qca_dlansky@qca.qualcomm.com>