Introduce libsmpputil

As part of preparation for libosmo-netif migration let's move common SMPP code
into separate build-time library and use it for both smpp_mirror and OsmoMSC
renaming the files if necessary.

While at it we also fix id/password legth limits in smpp_mirror and drop unused
fields from ESME struct.

Related: OS#5568
Change-Id: I61910651bc7c188dc2fb67d96189a66a47e7e8fb
diff --git a/configure.ac b/configure.ac
index 21056f9..41e51da 100644
--- a/configure.ac
+++ b/configure.ac
@@ -234,9 +234,11 @@
     include/Makefile
     include/osmocom/Makefile
     include/osmocom/msc/Makefile
+    include/osmocom/smpp/Makefile
     src/Makefile
     src/libmsc/Makefile
     src/libvlr/Makefile
+    src/libsmpputil/Makefile
     src/osmo-msc/Makefile
     src/utils/Makefile
     tests/Makefile