Allow creation of WiFi router proxies outside of WiFi Tests

This enables us to construct just a LinuxRouter, instead of depending on
the WiFiTestContextManager and LinuxRouter to handle this process.

TEST=network_WiFi_SimpleConnect.wifi_checkWPA_TKIP still passes
BUG=chromium:365879

Change-Id: I3d79b84aafb7262801b3b93125025cab0ad17488
Reviewed-on: https://chromium-review.googlesource.com/204744
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
3 files changed