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

.github/workflows/generate.yml

@@ -10,6 +10,6 @@ jobs:
     steps:
       - uses: actions/setup-go@v1
         with:
-          go-version: "1.17.4"
+          go-version: "1.17.6"
       - uses: actions/checkout@v2
       - run: go generate ./...