datapath-windows: Fixed packet limits on STT protocol

"If the length of the payload to be encapsulated exceeds 64KB, or if
the offset to the L4 header exceeds 255 bytes, then it will not be
possible to offload the packet to the NIC for segmentation." (STT RFC)
In this case the packet needs to be segmented by us, before sending it.

Signed-off-by: Paul-Daniel Boca <pboca@cloudbasesolutions.com>
Acked-by: Sairam Venugopal <vsairam@vmware.com>
Signed-off-by: Gurucharan Shetty <guru@ovn.org>