vortex restart debug : Kmm_a initialised at Kbb/Nbb for RK3 not at Kmm/Nnn ( Kmm/Nnn is an intermediary stage, it should not be meaningful at the beginning of a time step )

Remove silly change on mbku/mbkv/mbkf at the surface: this is useless
and is not compatible with 1 layer configurations (e.g. SWG and
ICE_AGRIF). Revert changes to namelists in ICE_AGRIF

Fix istate.F90 to avoid access to unallocated arrays in the SWE case. This change enables the SWG configuration to pass SETTE tests

RK3 time stepping branch formerly source:/NEMO/branches/2021/dev_r14318_RK3_stage1 updated on git with main. SETTE partly tested : problem with AGRIF_DEMO.