make: Build user_channel separately

We need to make sure that libuserlayer is installed before libipmi20
tries to install + relink. Otherwise the relink will fail causing the
build to sometimes fail. We can only guarantee this ordering safely by
using automake SUBDIRS since they are guaranteed to be executed in
order.

Change-Id: I6488eecb504f72273e97cfcf336e5bbd816c4137
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/configure.ac b/configure.ac
index 407c109..8d5e6dd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -167,5 +167,5 @@
 AC_DEFINE_UNQUOTED([HOST_IPMI_LIB_PATH], ["$HOST_IPMI_LIB_PATH"], [The file path to search for libraries.])
 
 # Create configured output
-AC_CONFIG_FILES([Makefile test/Makefile softoff/Makefile])
+AC_CONFIG_FILES([Makefile test/Makefile softoff/Makefile user_channel/Makefile])
 AC_OUTPUT