Add SocketUtils CTS tests

Test APIs below:
makeNetlinkSocketAddress(int, int)
makePacketSocketAddress(short, int)
makePacketSocketAddress(int, byte[])
closeSocket(java.io.FileDescriptor)

Bug:129200596
Test: atest FrameworksNetTests
      atest CtsNetTestCases --instant
Merged-In: I36252fdf516cf4a9d4506b615cdb38f5413739e5
(cherry picked from commit 93a53224d3a1cd6fc1de7d94955e03116b744e4a)

Change-Id: I0963acaf00c5bdd93db0503c426f190f409ca076

tests/net/common/java/android/net/util/SocketUtilsTest.kt

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.util;
+
+import android.system.NetlinkSocketAddress
+import android.system.Os
+import android.system.OsConstants.AF_INET
+import android.system.OsConstants.ETH_P_ALL
+import android.system.OsConstants.IPPROTO_UDP
+import android.system.OsConstants.RTMGRP_NEIGH
+import android.system.OsConstants.SOCK_DGRAM
+import android.system.PacketSocketAddress
+import androidx.test.filters.SmallTest
+import androidx.test.runner.AndroidJUnit4
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Assert.fail
+import org.junit.Test
+import org.junit.runner.RunWith
+
+private const val TEST_INDEX = 123
+private const val TEST_PORT = 555
+@RunWith(AndroidJUnit4::class)
+@SmallTest
+class SocketUtilsTest {
+    @Test
+    fun testMakeNetlinkSocketAddress() {
+        val nlAddress = SocketUtils.makeNetlinkSocketAddress(TEST_PORT, RTMGRP_NEIGH)
+        if (nlAddress is NetlinkSocketAddress) {
+            assertEquals(TEST_PORT, nlAddress.getPortId())
+            assertEquals(RTMGRP_NEIGH, nlAddress.getGroupsMask())
+        } else {
+            fail("Not NetlinkSocketAddress object")
+        }
+    }
+
+    @Test
+    fun testMakePacketSocketAddress() {
+        val pkAddress = SocketUtils.makePacketSocketAddress(ETH_P_ALL, TEST_INDEX)
+        assertTrue("Not PacketSocketAddress object", pkAddress is PacketSocketAddress)
+
+        val ff = 0xff.toByte()
+        val pkAddress2 = SocketUtils.makePacketSocketAddress(TEST_INDEX,
+                byteArrayOf(ff, ff, ff, ff, ff, ff))
+        assertTrue("Not PacketSocketAddress object", pkAddress2 is PacketSocketAddress)
+    }
+
+    @Test
+    fun testCloseSocket() {
+        // Expect no exception happening with null object.
+        SocketUtils.closeSocket(null)
+
+        val fd = Os.socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)
+        assertTrue(fd.valid())
+        SocketUtils.closeSocket(fd)
+        assertFalse(fd.valid())
+        // Expecting socket should be still invalid even closed socket again.
+        SocketUtils.closeSocket(fd)
+        assertFalse(fd.valid())
+    }
+}