fm10k: mbx_update_max_size does not drop all oversized messages
fm10k: mbx_update_max_size does not drop all oversized messages

When we call update_max_size it does not drop all oversized messages.
This is due to the difficulty in performing this operation, since it is
a FIFO which makes updating anything other than head or tail very
difficult. To fix this, modify validate_msg_size to ensure that we error
out later when trying to transmit the message that could be oversized.
This will generally be a rare condition, as it requires the FIFO to
include a message larger than the max_size negotiated during mailbox
connect. Note that max_size is always smaller than rx.size so it should
be safe to use here.

Also, update the update_max_size function header comment to clearly
indicate that it does not drop all oversized messages, but only those at
the head of the FIFO.

Signed-off-by: Jeff Kirsher <87e35f5be20bb3e67f4ba6b86f5f6be3085b1b3a@intel.com>
Signed-off-by: Jacob Keller <952d68dd7aa4b84e9f20381084cf63d55ea3c3b1@intel.com>
Acked-by: Matthew Vick <d265f499ad1500ed47610cc699ddce50365eb4ad@intel.com>
Tested-by: Krishneil Singh <c59b05ab42618d5787a42c35a821448b52690a31@intel.com>
Signed-off-by: Jeff Kirsher <87e35f5be20bb3e67f4ba6b86f5f6be3085b1b3a@intel.com>

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