Bump required cmake version to v3.16

Debian 11: cmake 3.18
Fedora 40: cmake 3.29
RHEL 9: installs cmake3, which is typically very recent, likely 3.29
Ubuntu 20: cmake 3.16

CMakeLists.txt

@@ -21,7 +21,7 @@
 
 # Author: laurent THOMAS, Lionel GAUTHIER
 
-cmake_minimum_required (VERSION 3.12)
+cmake_minimum_required (VERSION 3.16)
 project (OpenAirInterface LANGUAGES C CXX)
 
 #########################################################