utils: Fix compilation of the Wireshark plugin

There was no possibility to compile the Wireshark plugin because of an
enum class defined in MFSCommunication.h file. This file needs to be
readable for C89 compilers (which build the plugin). This commit makes
this definition invisible when compiling the plugin by surrounding it
with #ifdef __cplusplus.

Change-Id: I61df52baa1fca1b2462857f8b3a74c75291c1ed1