Change one message for maximum number of bathymetry points in STBTEL

In lecfon.f subroutine of STBTEL, the name of the keyword to be changed is wrong in a message: It should be MAXIMUM NUMBER OF BATHYMETRIC POINTS rather than NUMBER OF BATHYMETRIC POINTS (MAXIMUM is missing), for label 4020.

Remark raised by Noémie Durand.