batman-adv: tp_meter: avoid role confusion in tp_list

batman-adv: tp_meter: avoid role confusion in tp_list

Session lookups in tp_list matched only on destination address (and
optionally session ID), leaving role validation to the caller. If two
sessions with the same other_end coexisted (one as sender, one as receiver)
a lookup could silently return the wrong one, causing the caller's role to
bail out early, potentially skipping necessary cleanup.

Move the role check into the lookup functions themselves so the correct
entry is always returned, or none at all. Since batadv_tp_start()
legitimately needs to detect any active session to a destination regardless
of role, introduce a dedicated helper for that case rather than bending the
existing lookup semantics.

Cc: stable@kernel.org
Fixes: 33a3bb4a3345 ("batman-adv: throughput meter implementation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>