Added documentation for APIs in System.Net.Sockets introduced in 2.x (#3378)

* Added documentation for APIs in System.Net.Sockets introduced in 2.x

* Update xml/System.Net.Sockets/SocketTaskExtensions.xml

Co-Authored-By: Cory Nelson <[email protected]>

* Apply suggestions from code review

Co-Authored-By: Cory Nelson <[email protected]>

* Fix bug with param name;fix syntax;run acro

Author: jozkee