Introduce SCTP sockets support

SCTP is a transport layer protocol maintained by IETF and implemented in many Unix-like systems. It provides in-sequence reliable transport of data with congestion control like TCP and message-oriented like UDP. The design of SCTP includes multi-streaming and multi-homing capabilities.

The main goal of proposed approach is to make SCTP implementation based on existing TCP classes with adding a multi-stream concept on the abstract layer.

Code review is available on https://codereview.qt-project.org/95698