[PATCH net-next v2] net: stmmac: leave the datapath running for normal-size MTU changes

[Daniel Machon]

> When both MTUs are at most ETH_DATA_LEN, the receive buffer size and MAC
> receive limit do not change. Update the MTU without restarting the
> datapath.
> 
> This also avoids rebinding a live AF_XDP pool to a temporary RXQ. XDP
> rejects jumbo MTUs, so all supported XDP MTU changes take this path.
> Jumbo transitions still use the existing reopen path.
> 
> Found by source review while working on the stmmac MTU/resume recovery
> series. The fast path was tested on Allwinner H616 with sun8i EMAC1 and
> an AC300 PHY. The AF_XDP scenario was identified by inspection.

Reviewed-by: Daniel Machon <daniel.machon at microchip.com>