do not ignore build failures in subdirs of iproute2

if a file fails to compile in a subdir of iproute2 fails (say "tunnel.c" in
the "ip" dir), the top level makefile does not abort:
 all: Config
    @for i in $(SUBDIRS); \
    do $(MAKE) $(MFLAGS) -C $$i; done

the attached patch inserts a 'set -e' so that if the $(MAKE) fails, the all
target fails as well
-mike
diff --git a/Makefile b/Makefile
index 3fc3a15..dbcb249 100644
--- a/Makefile
+++ b/Makefile
@@ -32,7 +32,8 @@
 LIBNETLINK=../lib/libnetlink.a ../lib/libutil.a
 
 all: Config
-	@for i in $(SUBDIRS); \
+	@set -e; \
+	for i in $(SUBDIRS); \
 	do $(MAKE) $(MFLAGS) -C $$i; done
 
 Config: