IBDP: do less work by directly computing size

[dhalperi]

Stack:

• BgpProcess: only sort maps for JSON APIs #8907
• BgpRib: optimize multipath bestpaths #8906
• IBDP: do less work by directly computing size #8905 ⬅

⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.

[batfish-bot]

This change is 

[codecov]

Codecov Report

Merging #8905 (64065ba) into master (90aacc8) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8905      +/-   ##
==========================================
- Coverage   72.51%   72.50%   -0.02%     
==========================================
  Files        3319     3319              
  Lines      169420   169421       +1     
  Branches    19878    19878              
==========================================
- Hits       122854   122837      -17     
- Misses      37420    37435      +15     
- Partials     9146     9149       +3     

Files	Coverage Δ
.../org/batfish/dataplane/ibdp/BgpRoutingProcess.java	84.66% <100.00%> (ø)
...java/org/batfish/dataplane/ibdp/VirtualRouter.java	88.48% <100.00%> (ø)
...rc/main/java/org/batfish/dataplane/rib/BgpRib.java	90.04% <100.00%> (+0.04%)	⬆️

... and 5 files with indirect coverage changes

[SLarkworthy]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @anothermattbrown and @progwriter)