Add basic tests for <net/if.h>.

Bug: http://b/26447711
Change-Id: I9bbcdffc07e99c98e367a63de861ddc7b274d579
diff --git a/tests/Android.mk b/tests/Android.mk
index 0e84331..8e37a76 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -71,6 +71,7 @@
     malloc_test.cpp \
     math_test.cpp \
     mntent_test.cpp \
+    net_if_test.cpp \
     netdb_test.cpp \
     netinet_udp_test.cpp \
     pthread_test.cpp \