Add a ClearDeadline API

[schomatis]

go-libp2p-core/mux/mux.go

Lines 30 to 32 in 98f9714

	SetDeadline(time.Time) error
	SetReadDeadline(time.Time) error
	SetWriteDeadline(time.Time) error

(Same for read/write variants.)

[Stebalien]

Call SetDeadline(time.Time{}) to clear the timeout. See the interface documentation in https://golang.org/pkg/net/#Conn.

[schomatis]

Yeah, I'm aware of that, I had hope we could provide a more user-friendly API on this one.

[Stebalien]

I mean, we could, but then we'd have to implement it everywhere and we'd be deviating from the standard library at the same time. That's a lot of work/documentation for a papercut.

[schomatis]

Fair enough, if this has many repercussions throughout other repos is not worth it.