autotest: Convert WiFi beacon interval test to new framework

Remove the old beacon interval checking in WiFiMatFunc and replace it
with a new test in a more modern style.  Expand HostapConfig to
understand beacon intervals and site_linux_router to correctly interpret
the set interval.  Move the logic to check iw link values into
WiFiClient and delegate calls from site_wifitest to WiFiClient.

TEST=Ran successfully:
./run_remote_tests.sh --remote=chromeos1-shelf1-host4 check_bintval
./run_remote_tests.sh --remote=chromeos1-shelf1-host4 \
    network_WiFiMatFunc --args="test_pat=006*"
These verify the migrated test and that the iw link parsing delegation to
WiFiClient is working respectively.
BUG=chromium:230660

Change-Id: I2d7a2e07da33ac602faadadf02f95d473f75b91c
Reviewed-on: https://gerrit.chromium.org/gerrit/49774
Commit-Queue: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
8 files changed