Use correct generics for TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT in EpollChannelOption. Part of [#2396]

Motivation:
Currently the generics used for TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT are incorrect.

Modifications:
Use Integer as type

Result:
User can use TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT as expected