implement network driver on macOS

Description:
Using the 6.7.0 build from Homebrew on macOS, it doesn't seem to be possible to list nor add network configurations due to driver errors.

Replication:
Install libvirt from Homebrew and try to interact with any network settings.

$ brew install libvirt
$ sudo brew services start libvirt # starts successfully
$ sudo virsh -c qemu:///system net-list --all
error: Failed to get the number of active networks
error: this function is not supported by the connection driver: virConnectNumOfNetworks

Similarly, when trying to add any virtual network via virt-manager GUI (available for macOS here), another driver error is thrown:

Error creating virtual network: this function is not supported by the connection driver: virNetworkDefineXML

Based on this old issue with a similar error message, I tried brew edit libvirt, adding -Ddriver_network=enabled to the compile flags and then rebuilding via brew uninstall --ignore-dependencies libvirt && brew install -s libvirt, but the issue persists.

Context:
macOS version: tested both 10.13.6 (High Sierra) and 10.14.6 (Mojave)
libvirt version: 6.7.0 (from Homebrew)
libvirt build arguments: please see the Homebrew formula definition
virsh output:

$ virsh -V
Virsh command line tool of libvirt 6.7.0
See web site at https://libvirt.org/

Compiled with support for:
 Hypervisors: QEMU/KVM VMware VirtualBox ESX Test
 Networking: Remote Bridging
 Storage: Dir
 Miscellaneous: Daemon Secrets Debug Readline

Additional notes:
It's beyond cool that libvirt supports macOS as well, very thankful for all of your work.