Bluetooth: controller: Defer encryption setup if in conn update

Workaround, defer peer initiated encryption while local
initiated procedure with instant is not complete. Peer
master has sent CONN_UPDATE_IND in response to
CONN_PARAM_REQ, and also has initiated a Encryption Setup
thereafter. In this case, avoid corruption of the connection
update context by deferring the Encryption Setup.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>