Intel DPDK provides low level accleration by poll mode and huge page like infrastructure.
The top level TCP / UDP functionality, there are eco system partners who provide.
(ps: You can refer on http://www.dpdk.org/doc/api/rte__udp_8h.html for the udp header definition.)
Even though what you need is not clear, with the DPDK api, you can get the base address the packet itself.
Then by adjusting the offset, you can access the UDP payload of course.
If you need the protocol stack, then you should solution provided by some companies such as Tieto or WindRiver.