From: Sowmini Varadhan <redacted>
Date: Wed, 18 Apr 2018 09:47:06 -0400

- in the "GSO" proposal my 2000  bytes of data are sent as *two*
  udp packets, each of them with a unique udp header, and uh_len set
  to 1476 (for first) and 526 (for second). The receiver has no clue
  that they are both part of the same UDP datagram, So wire format
  is not the same, am I mistaken?

The sender is asking for two packets and this exact packetization,
that's why they explicitly set the socket option or provide the
cmsg value.

As Eric said, this is just exchanging N sendmsg() calls with 1.