Reworked optional JSON-C library support
Added missing export symbold


git-svn-id: https://svn.ntop.org/svn/ntop/trunk/nDPI@8170 a02cd0c1-8e76-42e1-a119-56f9641475e2
Minor fix


git-svn-id: https://svn.ntop.org/svn/ntop/trunk/nDPI@8171 a02cd0c1-8e76-42e1-a119-56f9641475e2
Minor fix


git-svn-id: https://svn.ntop.org/svn/ntop/trunk/nDPI@8172 a02cd0c1-8e76-42e1-a119-56f9641475e2