net/dante: try to unbreak the port's build on 15-CURRENT (+)

• Due to the way this code wraps around some standard library's functions, it cannot be compiled with -D_FORTIFY_SOURCE=2, so disable the naive check in the configure script
• Optionize UPnP support and remove SASL dependency for now as it does nothing alone; it could be introduced later together with proper LDAP support

Reported by: pkg-fallout