Respect mux.ErrReset in all Multiplexer implementations.

[Wondertan]

Background

Currently, relying on mux.ErrReset is not helpful and even useless, while cases for handling it do exist. Allmost all the mux.MuxedStream implementations return their own errors after Reset() or any internal connection issues:

• QUIC
• yamux
• mocknet

Only mplex returns mux.ErrReset, but that forces go-mplex to depend on go-libp2p-core (libp2p/go-yamux#6)

In addition, it might be helpful to define mux.ErrClosed to be returned on Write() after Close(), but it seems irrelevant cause of libp2p/go-libp2p-core#10

Resolving

All the listed multiplexers(except mocknet) have libp2p wrappers based in their own repos, so the solution is to redefine stream types in libp2p wrapping repos with checks of internal reset error to be replaced with mux.ErrReset, while mocknet may use it directly. Also, muxer testing suite should be updated to test for mux.ErrReset.

[Stebalien]

All merged. Thanks!