[WifiStress]Set Country code for 5G.

Bug: 80202599
Test: Local
Change-Id: I6a506ff14e4acb3c13c5ffc7e02a9d6dd01e09f3
diff --git a/acts/tests/google/wifi/WifiStressTest.py b/acts/tests/google/wifi/WifiStressTest.py
index 9e37061..863d4d5 100755
--- a/acts/tests/google/wifi/WifiStressTest.py
+++ b/acts/tests/google/wifi/WifiStressTest.py
@@ -242,6 +242,9 @@
             4. Verify softAP is turned down and WiFi is up.
 
         """
+        # Set country code explicitly to "US".
+        self.dut.droid.wifiSetCountryCode(wutils.WifiEnums.CountryCode.US)
+        self.dut_client.droid.wifiSetCountryCode(wutils.WifiEnums.CountryCode.US)
         ap_ssid = "softap_" + utils.rand_ascii_str(8)
         ap_password = utils.rand_ascii_str(8)
         self.dut.log.info("softap setup: %s %s", ap_ssid, ap_password)