If you want to search for packets being sent to a particular MAC address, you can just use wlan dst XX:XX:XX:XX:XX:XX if you want to search for packets being sent from a particular MAC address, you can just use wlan src XX:XX:XX:XX:XX:XX if you want to search for packets being sent to or from a particular MAC address, you can just use wlan host XX:XX:XX:XX:XX:XX. So just pass 0 as the 'net' argument to pcap_compile(). If the netmask of the network on which packets are being captured isn't known to the program, or if packets are being captured on the Linux 'any' pseudo-interface that can capture on more than one network, a value of 0 can be supplied tests for IPv4 broadcast addreses won't be done correctly, but all other tests in the filter program will be OK. The only place where the IP address matters is for ip broadcast filter expressions if you're not filtering for IPv4 broadcast addresses, which you probably won't be, there's no need to get the IPv4 address.

What airmon-ng did was to create a 'monitor' interface for the Wi-Fi adapter the regular network interface for the adapter might have an IP address assigned to it, but the monitor interface won't have one. All it means is that the network interface on which you're trying to capture does not have an IPv4 address assigned to it. 'no IPV4 address assigned' is an error from pcap_lookupnet().

Capture filter wireshark mac address