net: stmmac: RX buffer size must be 16 byte aligned

[ Upstream commit 8d558f02 ]

We need to align the RX buffer size to at least 16 byte so that IP
doesn't mis-behave. This is required by HW.

Changes from v2:
- Align UP and not DOWN (David)

Fixes: 7ac6653a

 ("stmmac: Move the STMicroelectronics driver")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>