ClatUtils - implement openNetlinkSocket()

Test: atest netd_unit_test
Bug: 65674744
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I652185296c8e92b5e4887e39baad8a3fec034cf7
diff --git a/server/ClatUtilsTest.cpp b/server/ClatUtilsTest.cpp
index 58ff95d..7fb0d5d 100644
--- a/server/ClatUtilsTest.cpp
+++ b/server/ClatUtilsTest.cpp
@@ -87,5 +87,11 @@
     close(fd);
 }
 
+TEST_F(ClatUtilsTest, TryOpeningNetlinkSocket) {
+    int fd = openNetlinkSocket();
+    ASSERT_LE(3, fd);
+    close(fd);
+}
+
 }  // namespace net
 }  // namespace android