enum AlphaIndex

RTO alpha index.

References from:: SctpProfile;

`1`	`ALPHA_1_2ND` ALPHA_1_2ND -> RTO.Alpha=1/2.
`2`	`ALPHA_1_4TH` ALPHA_1_4TH -> RTO.Alpha=1/4.
`3`	`ALPHA_1_8TH` ALPHA_1_8TH -> RTO.Alpha=1/8.
`4`	`ALPHA_1_16TH` ALPHA_1_16TH -> RTO.Alpha=1/16.