contrib/osmo-msc.spec.in: Enable SMPP in RPM builds

The SPEC file already included a build dependency to libsmpp34, but
then the compilation of osmo-msc didn't actually pass --enable-smpp
along, resulting in binaries without SMPP support - unlike the Debian
binaries, which do contain that part.

Change-Id: I223be7a735e97b32f7c0ff246cf826f109b0f686

contrib/osmo-msc.spec.in

@@ -77,6 +77,7 @@ autoreconf -fi
 %if %{with_iu}
   --enable-iu \
 %endif
+  --enable-smpp \
   --docdir=%{_docdir}/%{name} \
   --with-systemdsystemunitdir=%{_unitdir}