Move send_tun into tun.c as well.

Also remove a redundant include in checksum.c.

Change-Id: I0b8858343b1496f22904d3b316b6c435be0f648a
diff --git a/Android.mk b/Android.mk
index 819c86f..bdb9317 100644
--- a/Android.mk
+++ b/Android.mk
@@ -30,7 +30,7 @@
 
 LOCAL_MODULE := clatd_test
 LOCAL_CFLAGS := -Wall -Werror -Wunused-parameter
-LOCAL_SRC_FILES := clatd_test.cpp dump.c checksum.c translate.c icmp.c ipv4.c ipv6.c logging.c
+LOCAL_SRC_FILES := clatd_test.cpp dump.c checksum.c translate.c icmp.c ipv4.c ipv6.c logging.c tun.c
 LOCAL_MODULE_TAGS := eng tests
 LOCAL_SHARED_LIBRARIES := liblog