net/http: enable HTTP/2 on all Transports, not just the DefaultTransport
This mirrors the same behavior and API from the server code to the
client side: if TLSNextProto is nil, HTTP/2 is on by default for
both. If it's non-nil, the user was trying to do something fancy and
step out of their way.
Updates #6891
Change-Id: Ia31808b71f336a8d5b44b985591d72113429e1d4
Reviewed-on: https://go-review.googlesource.com/17300 Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>