tests: Bluetooth: Tester: Handle BIGInfo after sync request

In the BAP Broadcast Sink implementation the sync request,
the BIGInfo and the broadcast code can come in any other.
Currently the btp_bap_broadcast_sink_bis_sync would reject
the request if it came before the BIGInfo, but will now
instead store the request and then apply it once the BIGInfo
has been received, as there is not BIGInfo BTP event that the
caller can use.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>