Update layerThickness halos after advection

Update layerThickness halos after advection. This reduces the error
in a test with 500 m/yr face-melt, so it seems to be necessary, but
it does not solve the issue entirely.

components/mpas-albany-landice/src/mode_forward/mpas_li_advection.F

@@ -560,6 +560,10 @@ subroutine li_advection_thickness_tracers(&
             enddo
          endif
 
+         ! Update halos after advection.
+         call mpas_timer_start("halo updates")
+         call mpas_dmpar_field_halo_exch(domain, 'layerThickness')
+         call mpas_timer_stop("halo updates")
 
          ! Calculate dynamicThickening (layerThickness is updated by advection at this point, while thickness is still old)
          dynamicThickening = (sum(layerThickness, 1) - thickness) / dt * scyr  ! units of m/yr