RFR [12] 8209454: [error-prone] TypeParameterUnusedInFormals in jdk.net

[Chris Hegarty]

The declaration of the implementation private method `checkValueType`,
has a misuse of generics by only using a naked type parameter as a
return type. One solution is to ensure that the return type is a subtype
of the known SocketFlow type, by passing the expected class literal.

http://cr.openjdk.java.net/~chegar/8209454.00/

-Chris.