UDP GRO do not restore ervery UDP Packet

[Sean Tong]

I find that I do not restore every UDP paket from recvmsg when I
programming with  UDP_GRO in kernel version 5.0
I can get gso_size, but I do not know the last UDP packet size in
aggregate datagram.
For example, recvmsg returns  a packet size 50  of  and gso_size of
24, so the UDP packets is restored without knowing whether it is
24+24+2 split into 3 packets or 24+26 split into 2 pakcets.
Is there any way to get the last UDP packet size or number of merged
UDP packets?