pcap_set_rfmon(3pcap) on macOS

The text ddfa92c04031, as macOS 10.14.6, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

set monitor mode for a not-yet-activated capture handle

pcap_set_rfmon(3pcap) on macOS now