SMPP USSD Mica ussd_service_op codes are incorrect.

Currently the Mica ``ussd_service_op`` codes are incorrect. The list of supported op codes is incomplete and some of the existing codes confuse the hexidecimal and decimal values. The correct list of values should be:
```
1 (0x01) PSSR indication // start deliverSm -- BEGIN
2 (0x02) USSR request // sumbmitSm -- CONT
17 (0x11) PSSR response // sumbmitSm -- END
18 (0x12) USSR confirm // deliverSm -- CONT 
129 (0x81) USSREL indication // deliverSm -- ABORT
```
For symmetry, we should define these in decimal and convert to hexadecimal where we use them.