enum BetaIndex

RTO beta index.

References from:: SctpProfile;

`1`	`BETA_1_2ND` BETA_1_2ND -> RTO.Beta = 1/2.
`2`	`BETA_1_4TH` BETA_1_4TH -> RTO.Beta = 1/4.
`3`	`BETA_1_8TH` BETA_1_8TH -> RTO.Beta = 1/8.
`4`	`BETA_1_16TH` BETA_1_16TH -> RTO.Beta = 1/16.

enum BetaIndex