Generic XDP coexistence with NBL offloads

[mtfriesen]

Generic XDP needs to be compatible with:

RSC offload - send OID to disable when non-RSC-aware programs/XSKs are attached
Checksum offload - fix up checksum header fields when *ChecksumValueInvalid bits are set in OOB.

Plan for RSC offload:

1. Add minimal RSC -> LSO direct conversion - assume LSO is directly convertible
   a. NBL+NB pool
   b. clear IPv4 csum and set TCP pseudoheader csum
   c. add functional test

2. Add LSO configuration awareness
   a. maintain current offload state
   b. drop RSC packets > LSO max or < min segments
   c. add drop statistics
   d. add functional test

3. Add RSC -> LSO partial segmentation
   a. copy L2-L4 headers into preallocated NBL
   b. copy data partial MDL into preallocated partial MDL
   c. fix up TCP flags and seq numbers
   d. read the LSO spec - what else do we need?
   e. add SW segmentation statistics
   f. add functional test

4. spinxsk test
   a. produce random RSC packets

5. perf test
   a. onboard to netperf