SMPP: add small utility program 'smpp_mirror'

This program binds as ESME transceiver to a SMSC and simply mirrors back
all SMS that it receives.
diff --git a/openbsc/src/utils/Makefile.am b/openbsc/src/utils/Makefile.am
index c5b6a7a..701e9b8 100644
--- a/openbsc/src/utils/Makefile.am
+++ b/openbsc/src/utils/Makefile.am
@@ -4,6 +4,10 @@
 
 bin_PROGRAMS = bs11_config isdnsync
 
+if BUILD_SMPP
+noinst_PROGRAMS = smpp_mirror
+endif
+
 bs11_config_SOURCES = bs11_config.c
 bs11_config_LDADD = $(top_builddir)/src/libcommon/libcommon.a \
 		    $(top_builddir)/src/libbsc/libbsc.a \
@@ -11,3 +15,7 @@
 		    $(LIBOSMOCORE_LIBS) $(LIBOSMOGSM_LIBS) $(LIBOSMOABIS_LIBS)
 
 isdnsync_SOURCES = isdnsync.c
+
+smpp_mirror_SOURCES = smpp_mirror.c
+smpp_mirror_LDADD = $(top_builddir)/src/libcommon/libcommon.a \
+		    $(LIBOSMOCORE_LIBS) $(LIBSMPP34_LIBS)