mpih_set_cond: restore EM leakage mitigation
* mpi/mpih-const-time.c (_gcry_mpih_set_cond): Replace single mask + XOR with dual mask + AND/OR; Add comment about reason for dual mask usage. (_gcry_mpih_add_n_cond, _gcry_mpih_sub_n_cond, _gcry_mpih_swap_cond) (_gcry_mpih_abs_cond): Add comment about reason for dual mask usage.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>