cmd/cgo/internal/test: only test specific frames in testCallbackCallersSEH

cmd/cgo/internal/test: only test specific frames in testCallbackCallersSEH

testCallbackCallersSEH will break if anything in this call chain is
refactored to have a different number of function calls.

This change makes the test more robust by only testing the frames
that are actually relevant to the test.

Change-Id: Idb51514d7079f55da6e6ddc52ad43b1ffe32c8c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/545755
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>