chore: use go1.17.6 (#664)

We're starting to prepare a new release. The first step is to use
go1.17.6 in the following places:

1. everywhere we define the version of Go in this tree;

2. when we're building for Android (using ooni/go);

3. in our ooni/oohttp fork of Go net/http standard library.

Reference issue: https://github.com/ooni/probe/issues/1845

mk

@@ -64,7 +64,7 @@ GOLANG_EXTRA_FLAGS =
 
 #help:
 #help: * GOLANG_VERSION_NUMBER : the expected version number for golang.
-GOLANG_VERSION_NUMBER = 1.17.4
+GOLANG_VERSION_NUMBER = 1.17.6
 
 #help:
 #help: * MINGW_W64_VERSION     : the expected mingw-w64 version.
@@ -72,7 +72,7 @@ MINGW_W64_VERSION = 10.3.1
 
 #help:
 #help: * OONIGO_BRANCH         : the github.com/ooni/go branch to use.
-OONIGO_BRANCH = oonigo1.17
+OONIGO_BRANCH = oonigo1.17.6
 
 #help:
 #help: * OONI_PSIPHON_TAGS     : build tags for `go build -tags ...` that cause