Bluetooth: Mesh: Disable randomization in DFD model for canceling update

Disable randomization in the access layer when cancelling update in the
distribution server model. This is needed because the server sends 2
messages in a row and the gets reordered by the access layer
randomization feature making DFU/SR/FD/BV-43-C test to fail.

This fixes DFU/SR/FD/BV-43-C test.

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>