The MAC in the the H7 has it's own dedicated internal DMA, so I don't think that disabling the system-wide DMA would have any effect. I can give it a shot anyways though and report back!
One thing I am wondering is if you have properly set up the MAC address filtering. For TCP, each peer advertises its supported MSS (read MTU) and any connected peer should never send a packet that exceeds that negotiated MTU. That limiting should prevent TCP packets from overflowing a tiny, 590 byte buffer.
It does nothing for broadcast or UDP packets, however. But those do not tend to be so large as streaming TCP data which will normally transmits data at the negotiated maximum size.
But if you are not properly filtering incoming addresses, then you are also receiving packets that are are not destined for you and hence will not obey the negotiated maximum.
May sure that PROMISCUOUS mode and other other more obscure filter options are disabled.
