net: fix typo in ctrlCtxFn parameter name

net: fix typo in ctrlCtxFn parameter name

context.Context parameters are commonly named ctx, not cxt.

Change-Id: Icaadbcd38b054694959e5e8a058552a3e54be6d4
Reviewed-on: https://go-review.googlesource.com/c/go/+/586016
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>