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