net: atlantic: verify hw_head_ lies within TX buffer ring

[ Upstream commit 2120b7f4d128433ad8c5f503a9584deba0684901 ]

Bounds check hw_head index provided by NIC to verify it lies
within the TX buffer ring.

Reported-by: Aashay Shringarpure <aashay@google.com>
Reported-by: Yi Chou <yich@google.com>
Reported-by: Shervin Oloumi <enlightened@google.com>
Signed-off-by: Grant Grundler <grundler@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>