nrfconnect: Fix printing BLE error on regular session disconnection. (#4722)
nrfconnect: Fix printing BLE error on regular session disconnection. (#4722)

Regular disconnection after network provisioning is treated
as BLE error and confusing message is printed.

* Added checking if connection is disconnected after successful
provisioning to detect whether it was intended.
nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,nestlabs/connectedhomeip,project-chip/connectedhomeip,project-chip/connectedhomeip