Fix ABL boundary planes inflow when using multiple levels

[marchdf]

If more than one level is present, reading inflow boundary conditions from higher levels leads to spurious velocities at the coarse-fine interface (see image). Disabling the velocity solve does not fix the issue. Disabling the nodal projection does fix the issue. It is unclear where this issue comes from. The initial thought was this came from ghost cells not being filled correctly at the fine level. This may not be the case... Currently the code aborts if the user tries to use multiple levels for inflow.