This fixes it up so that the driver actually works on things like
AP_Periph that poll at a high rate. This was never a problem with the
main firmware as EFI was run at a lower rate, but on AP_Periph this was
much to fast. This lead to spamming fresh requests and keeping the
buffer completly stuffed with requests. To compound it, the EFI device
would start over when there was a fresh request, and eventually our
buffer writes become corrupted leading to bad checksums, and a complete
failure of the comms. This prevents that situation from happening.
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