Add a CU-UP load tester and improve GTP performance
This adds a simple tester program for the CU-UP. It sets up a number of
UEs/bearers in the CU-UP via the E1 interface, then streams data in
downlink/uplink (as seen by the CU-UP). More information is available in
tests/nr-cuup/README.md.
Includes some fixes to properly verify that SCTP is installed, and use
"the right cmake way" to use it in cmake code (see commit for details).
Jaroslava Fiedlerova
d630fb2965