OffloadUtils - implement getTetherIngressMapFd()

Test: build, atest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ie18e296f234594ef02f91418f258f2ab105de48e
diff --git a/server/OffloadUtilsTest.cpp b/server/OffloadUtilsTest.cpp
index e04b3c0..a893588 100644
--- a/server/OffloadUtilsTest.cpp
+++ b/server/OffloadUtilsTest.cpp
@@ -113,6 +113,14 @@
     close(fd);
 }
 
+TEST_F(OffloadUtilsTest, GetTetherIngressMapFd) {
+    SKIP_IF_BPF_NOT_SUPPORTED;
+
+    int fd = getTetherIngressMapFd();
+    ASSERT_LE(3, fd);  // 0,1,2 - stdin/out/err, thus 3 <= fd
+    close(fd);
+}
+
 TEST_F(OffloadUtilsTest, TryOpeningNetlinkSocket) {
     int fd = openNetlinkSocket();
     ASSERT_LE(3, fd);