Bluetooth: Mesh: Fix missing protocol error timeout

Provisioning errors shouldn't cause device to close link. Upon error,
device will send Provisioning Failed PDU, and any further PDU's will
be considered as unexpected as per Mesh Profile section 5.4.4.

Also a timer is started every time device sends or receives a PDU.
This affects MESH/NODE/PROV/BV-10-C test case.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>