Bluetooth: controller: Fix pdu being overwritten while in use

The node_rx buffer for the connect ind buffer is being reused to send
connection complete event, make sure all data is backed up before
reusing the buffer.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>
Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>