tests: Add an IPv4 loopback address of 127.0.0.1/8 to the lo0

interface by default when creating VNETSs using pytest.

Reviewed By: asomers
Differential Revision: https://reviews.freebsd.org/D38021

tests/atf_python/sys/net/vnet.py

@@ -92,6 +92,7 @@ def run_cmd(
     def setup_loopback(cls, vnet_name: str):
         lo = VnetInterface("", "lo0")
         lo.set_vnet(vnet_name)
+        lo.setup_addr("127.0.0.1/8")
         lo.turn_up()
 
     @classmethod