TDLS: Fix TDLS Setup Request processing in existing-peer cases

TDLS: Fix TDLS Setup Request processing in existing-peer cases

wpa_tdls_peer_free() ended up getting called after some of the
parameters from the TDLS Setup Request frame were copied into the struct
wpa_tdls_peer information. This could result in continuing with cleared
information in case the new exchange was the one that is used in
concurrent initialization case or if this is to re-negotiated an
existing TDLS link. The driver would not be provided with all the peer
capabilities correctly in such case.

Fix this by moving the existing_peer check to happen before the
information from the TDLS Setup Request frame is copied.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>