Bluetooth: Mesh: Add option to call update cb on every retransmission

A user may want to control message parameters (for example, delay
parameter) on every retransmission of a published message (for example,
see section 1.4.1 of the mesh model specification). This is essential
for lighting messages as time gap between messages retransmitted via
the publish-retransmit mechanism introduces unwanted jitter/pop-corn
when such retransmissions are received by a large 'group' of lights.

This commit adds an option to `struct bt_mesh_model_pub` to make the
access layer call `bt_mesh_model_pub.update` callback on every
retransmission. This also addes few macros and functions that can be
used for further calculations.

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