net: stmmac: use correct DMA buffer size in the RX descriptor

net: stmmac: use correct DMA buffer size in the RX descriptor

[ Upstream commit 583e6361414903c5206258a30e5bd88cb03c0254 ]

We always program the maximum DMA buffer size into the receive descriptor,
although the allocated size may be less. E.g. with the default MTU size
we allocate only 1536 bytes. If somebody sends us a bigger frame, then
memory may get corrupted.

Fix by using exact buffer sizes.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>