Introduce program gtp-echo-responder

This is a small standalone program (under MIT license, hence cannot make
use of libosmocore) whose only purpose is to answer GTPC (v1 and v2)
Echo Request messages with Echo Reply ones, with information provided
from the command line.

A small python script companion is provided to easily test the program.

Related: SYS#5598
Change-Id: Ibdd6d8f6920571db0c60cf8b3b25d541b15ad3f1
diff --git a/contrib/osmo-ggsn.spec.in b/contrib/osmo-ggsn.spec.in
index 6d55af8..bee8fc1 100644
--- a/contrib/osmo-ggsn.spec.in
+++ b/contrib/osmo-ggsn.spec.in
@@ -61,6 +61,15 @@
 This subpackage contains libraries and header files for developing
 applications that want to make use of libgtp.
 
+%package -n gtp-echo-responder
+Summary:        Small program answering GTP ECHO Request with GTP ECHO Response
+License:        MIT
+Group:          System/Libraries
+
+%description -n gtp-echo-responder
+Small program answering GTP ECHO Request with GTP ECHO Response for both GTPCv1
+and GTPCv2.
+
 %prep
 %setup -q
 
@@ -122,4 +131,7 @@
 %{_libdir}/libgtp.so
 %{_libdir}/pkgconfig/libgtp.pc
 
+%files -n gtp-echo-responder
+%{_bindir}/gtp-echo-responder
+
 %changelog