remove explicit `selector` field in TcpConnection + TcpListener
Revert "Change socket options type from `immutable.Traversable` to `Traversable`"

This reverts commit ba922fa2d75be264de9063326d99fae3f3b57191.

Conflicts:
	akka-io/src/main/scala/akka/io/Tcp.scala
	akka-io/src/main/scala/akka/io/TcpIncomingConnection.scala
	akka-io/src/main/scala/akka/io/TcpListener.scala
	akka-io/src/main/scala/akka/io/TcpOutgoingConnection.scala