Bluetooth: Check for valid bdaddr in add_remote_oob_data

Before doing any other verifications, the add_remote_oob_data function
should first check that the given address is valid. This patch adds such
a missing check to the beginning of the function.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>