build: enable unit-tests

Enable unit-tests in the configure and makefile.

Tested: Compiled.
Change-Id: I8a573bb97c4752254797104c75660ecd372fb120
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index ac68e5e..218ea38 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -12,3 +12,5 @@
 libethstatscmd_la_CXXFLAGS = \
 	$(LIBIPMID_CFLAGS) \
 	-flto
+
+SUBDIRS = . test