pkgconfig: gnutls jsoncpp, openssl are public dependencies

opendht.pc.in

@@ -7,5 +7,6 @@ Description: C++17 Distributed Hash Table library
 Version: @VERSION@
 Libs: -L${libdir} -lopendht
 Libs.private: @http_parser_lib@ -pthread
-Requires.private: gnutls >= 3.3, nettle >= 2.4@argon2_lib@@jsoncpp_lib@@openssl_lib@
+Requires: gnutls >= 3.3@jsoncpp_lib@@openssl_lib@
+Requires.private: nettle >= 2.4@argon2_lib@
 Cflags: -I${includedir}