[vlan] Use "-" instead of "." as separator in VLAN device names

VLAN device names have the form "netX.Y", e.g. "net0.5" for VLAN 5 on
net0.  This use of "." conflicts with the use of "." as the
hierarchical separator in settings block names, with the result that
VLAN device settings cannot be accessed by name.

It would be trivial to treat the VLAN device settings as being a child
of the trunk device settings, but this would cause the VLAN device
settings to be applied to the trunk device: for example, setting
"net0.5/ip" would then apply the IP address to both net0.5 and net0.

Fix by changing the VLAN device name to use "-" instead of ".": the
VLAN device "net0.5" is now "net0-5".

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/vlan.c

 	vlan->priority = priority;
 
 	/* Construct VLAN device name */
-	snprintf ( netdev->name, sizeof ( netdev->name ), "%s.%d",
+	snprintf ( netdev->name, sizeof ( netdev->name ), "%s-%d",
 		   trunk->name, vlan->tag );
 
 	/* Register VLAN device */