PMI and MCS table index in phy-test (#182)

Add options to set PMI and MCS table index in phy-test:
- Precoding Matrix Index (PMI): -p <pmi>
- DL MCS table index: -n <index>
- UL MCS table index: -u <index>
Reviewed-by: Robert Schmidt <robert.schmidt@openairinterface.org>
Reviewed-by: Laurent THOMAS <laurent.thomas@open-cells.com>