Adding min_sdk_version to libevent required for bt apex

Bug: 206121418
Test: Compile
Change-Id: Ib3cc790a8ed50df3f092d166cc4c95317e947738
diff --git a/Android.bp b/Android.bp
index 1253379..5b019d0 100644
--- a/Android.bp
+++ b/Android.bp
@@ -116,4 +116,5 @@
             srcs: ["kqueue.c"],
         },
     },
+    min_sdk_version: "30",
 }