Correct restartability issues for RK3+ISF
WED025 and ISOMIP+ are not restartable when running with key_RK3. The problem comes from tra_isf.
- stprk3 calls isf_stp(Nbb) It sets risf_cav_tsc_b i.e. n-1 and comptes risf_cav_tsc i.e. n at the beginning of each time step
- stprk3_stg calls tra_isf(Kmm, Krhs) It updates ts @ Krhs with T & S ice shelf contribution based on risf_cav_tsc and risf_cav_tsc_b half sum (Kmm is only used for coupling).
RK3 does not uses fields at n-1 so only risf_cav_tsc should be used in tra_isf when key_RK3 is active. Any use/update of risf_cav_tsc_b should be remove.
It suggest we don't need and restart mechanism when key_RK3 is active.
TO DO : check with GM & PM tra_isf Kmm index