Add new F1AP msg enc&dec library

Add a new target f1ap_lib that groups F1AP ASN.1 encoding&decoding for
messages defined f1ap_messages_types.h. The objective is to, for each
F1AP message,
- add encoder&decoder (similar to what already exists, but without
  mandatory message sending afterwards)
- eq_X() function that checks two messages for equality (to be used
  mostly in tests)
- cp_X() function that deep-copies a message, e.g., to be used when
  sending ITTI messages, instead of manual copying done currently
- free_X() function that frees the memory associated to a memory, to
  avoid memory leaks.

Each message will be tested, notably that encoding&decoding as well as
copying yield identical messages.

The actual message encoding & decoding, tests, and their use will be
done in the forthcoming commits.

openair2/F1AP/tests/CMakeLists.txt

@@ -0,0 +1,6 @@
+add_executable(f1ap_lib_test f1ap_lib_test.c)
+add_dependencies(tests f1ap_lib_test)
+add_test(NAME f1ap_lib_test COMMAND f1ap_lib_test)
+target_link_libraries(f1ap_lib_test PRIVATE f1ap_lib)
+target_link_libraries(f1ap_lib_test PRIVATE asn1_f1ap)
+target_include_directories(f1ap_lib_test PRIVATE ${CMAKE_SOURCE_DIR})