[backport v1.14] Bluetooth: Mesh: Move RPL clear to bt_mesh_reset

Moves the clearing of RPL out of the bt_mesh_rx_reset() to avoid it
being called outside of the node reset procedure.

Fixes #29858 for v1.14.

Signed-off-by: Trond Einar Snekvik <Trond.Einar.Snekvik@nordicsemi.no>