Fail large requests with EFBIG.

The adapter firmware in general does not accept PDUs larger than 64k - 1
bytes in size. Sending crypto requests larger than this size result in
hangs or incorrect output, so reject them with EFBIG. For requests
chaining an AES cipher with an HMAC, the firmware appears to require
slightly smaller requests (around 512 bytes).

Sponsored by: Chelsio Communications