Import wifi_channel_stat into legacy_hal namespace.

Fixes android.hardware.wifi@1.0-service-tests build failure.

Change-Id: I067106c4db8a9c9c358ec287409cc1b93c50c926
diff --git a/wifi/1.4/default/wifi_legacy_hal.h b/wifi/1.4/default/wifi_legacy_hal.h
index 1652ae9..822f83a 100644
--- a/wifi/1.4/default/wifi_legacy_hal.h
+++ b/wifi/1.4/default/wifi_legacy_hal.h
@@ -271,6 +271,7 @@
 using ::wifi_band;
 using ::wifi_cached_scan_results;
 using ::wifi_channel_info;
+using ::wifi_channel_stat;
 using ::wifi_channel_width;
 using ::wifi_error;
 using ::wifi_gscan_capabilities;