Missplacing of the call to lbc_lnk in the bdy_tra

[epico]

Analyzing the source code, a potential bug has been identified in bdy_tra.
The lbc_lnk is invoked outside the loop on nb_bdy. The processes will exchange after having locally updated the values on the boundaries. This works fine if the new values on the boudaries do not depend from the adjacent points. For some schemas, such as bdy_tra_nmn and bdy_tra_rnf, this is not true.
The bug could happen when nb_dby is greater then 1 and bdy_tra_nmn or bdy_tra_rnf is used.

Moreover in the 3.5a version a new optimized routine (lbc_bdy_lnk) for handling the communication during the BDY has been introduced.

Finally, the last input parameter (ib_bdy) and the calls to the lbc_bdy_lnk can be removed from the routine bdy_tra_frs

The bdy_tra could be modified as follow:

      DO ib_bdy=1, nb_bdy
    
         SELECT CASE( nn_tra(ib_bdy) )
         CASE(jp_none)
            CYCLE
         CASE(jp_frs)
            CALL bdy_tra_frs( idx_bdy(ib_bdy), dta_bdy(ib_bdy), kt )
         CASE(2)
            CALL bdy_tra_spe( idx_bdy(ib_bdy), dta_bdy(ib_bdy), kt )
         CASE(3)
            CALL bdy_tra_nmn( idx_bdy(ib_bdy), dta_bdy(ib_bdy), kt )
         CASE(4)
            CALL bdy_tra_rnf( idx_bdy(ib_bdy), dta_bdy(ib_bdy), kt )
         CASE DEFAULT
            CALL ctl_stop( 'bdy_tra : unrecognised option for open boundaries for T and S' )
         END SELECT

         CALL lbc_bdy_lnk( tsa(:,:,:,jp_tem), 'T', 1., ib_bdy )
         CALL lbc_bdy_lnk( tsa(:,:,:,jp_sal), 'T', 1., ib_bdy )
      ENDDO