Changes

sctp_server: fix state in catch-all handle_call()

Sending an unexpected call breaks the server, because the third member
of a returned tuple (not_implemented) becomes the new state.  It was
actually meant to be part of the Reply - fix this.

https://www.erlang.org/doc/apps/stdlib/gen_server.html#c:handle_call/3

  {reply, Reply :: term(), NewState :: term()}

Change-Id: I1cc683e549c3bb61e3e4c45bb3d244202d61be53