r8153_ecm: Add Lenovo Powered USB-C Hub as a fallback of r8152

This commit enables the use of the r8153_ecm driver, introduced with
commit c1aedf01

 ("net/usb/r8153_ecm: support ECM mode for
RTL8153") for the Lenovo Powered USB-C Hub (17ef:721e) based on the
Realtek RTL8153B chip.

This results in the following driver preference:

- if r8152 is available, use the r8152 driver
- if r8152 is not available, use the r8153_ecm driver

This is done to prevent the NIC from constantly sending pause frames
when the host system enters standby (fixed by using the r8152 driver
in "r8152: Add Lenovo Powered USB-C Travel Hub"), while still allowing
the device to work with the r8153_ecm driver as a fallback.

Signed-off-by: Leon Schuermann <leon@is.currently.online>
Tested-by: Leon Schuermann <leon@is.currently.online>
Link: https://lore.kernel.org/r/20210111190312.12589-3-leon@is.currently.online
Signed-off-by: Jakub Kicinski <kuba@kernel.org>