xds/googlec2p: use xdstp names for LDS

[apolcyn]

As title.

Integration tests passing.

RELEASE NOTES:

• xds/googlec2p: use xdstp names for LDS

[codecov]

Codecov Report

Merging #6949 (06e693d) into master (8d735f0) will decrease coverage by 0.02%.
Report is 1 commits behind head on master.
The diff coverage is 68.96%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6949      +/-   ##
==========================================
- Coverage   83.71%   83.69%   -0.02%     
==========================================
  Files         287      287              
  Lines       30926    30929       +3     
==========================================
- Hits        25889    25887       -2     
- Misses       3972     3976       +4     
- Partials     1065     1066       +1     

Files	Coverage Δ
balancer/grpclb/grpclb.go	80.47% <ø> (ø)
balancer/grpclb/grpclb_remote_balancer.go	83.69% <ø> (ø)
balancer/rls/config.go	83.22% <100.00%> (ø)
encoding/proto/proto.go	62.50% <ø> (ø)
internal/binarylog/method_logger.go	87.31% <100.00%> (ø)
internal/binarylog/sink.go	11.42% <ø> (ø)
internal/pretty/pretty.go	57.89% <100.00%> (+15.78%)	⬆️
internal/status/status.go	90.52% <100.00%> (ø)
internal/transport/handler_server.go	85.91% <ø> (ø)
internal/transport/http2_server.go	89.56% <ø> (ø)
... and 15 more

... and 14 files with indirect coverage changes

[arvindbr8]

Looks good!