<sys/un.h>: add SUN_LEN.

Also used by lldb.

Bug: N/A
Test: ran tests
Change-Id: I4c2aa60e7a3d8c691742c12ebde142d9438bf60f
diff --git a/tests/Android.bp b/tests/Android.bp
index 00f2856..b504fa1 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -167,6 +167,7 @@
         "sys_ttydefaults_test.cpp",
         "sys_types_test.cpp",
         "sys_uio_test.cpp",
+        "sys_un_test.cpp",
         "sys_vfs_test.cpp",
         "sys_xattr_test.cpp",
         "system_properties_test.cpp",