support the case of no enp0 if is present

if seems on ionopimax, with predictable network IF on, the
main (only) interface is named enx....... instead of end0
this is a fix to support it

utils.py

@@ -98,6 +98,14 @@ class BoxInfo:
                 if ifname in ('eth0', 'enp1s0', 'end0'):
                     macaddr = addr
                     self.main_if = ifname
+        if self.main_if is None:
+            if len(self.network_interfaces) == 1:
+                self.main_if = list(self.network_interfaces)[0]
+                macaddr = self.network_interfaces[self.main_if]
+            elif self.network_interfaces:
+                raise RuntimeError(f'ambiguous main if: {self.network_interfaces}')
+            else:
+                raise RuntimeError('no main if found')
         self.macaddr = macaddr
         if macaddr:
             self.id = int(''.join(macaddr.split(':')[-3:]), 16) & 0xffffff