`MAX_RADIUS_deg` is not general enough for a non longitude latitude
grid. The variable `max_radius` moves from module `input_ssh_m` to
module `config_m`. The variable `MAX_RADIUS_deg` disappears. The
constraint `2 * max_radius_deg(1) < 180` becomes `4 * max_radius(1) <
nlon` but is only applied to the periodic case because we do not have
the general equivalent of 180° in number of points.