multiple configurables with the same `name` method can result in :(

[yomimono]

See https://github.com/yomimono/mirage/commit/aefa0ada48e8c013a3d418cc2f09689ebaa51728 for a commit reproducing the problem and a description. Note that ipv4_qubes_conf (https://github.com/yomimono/mirage/blob/aefa0ada48e8c013a3d418cc2f09689ebaa51728/lib/mirage.ml#L710) and ipv4_dhcp_conf, (https://github.com/yomimono/mirage/blob/aefa0ada48e8c013a3d418cc2f09689ebaa51728/lib/mirage.ml#L668) have the same name field.