Summary:
The GSO write path in LibevQuicAsyncUDPSocket falls back to
single-packet writes when sendmsg with UDP_SEGMENT fails with EIO or
EINVAL. This adds EMSGSIZE to the fallback.

Reviewed By: kvtsoy

Differential Revision: D96937735

fbshipit-source-id: 2f880290edf01ce04e0edbc6c4fafcaacf1851ac