BDDPacket: when converting to Flow, constrain to sane packets

[dhalperi]

IP packets and L4 protocols have some constraints. E.g., all IP packets are at
least 20 bytes. Enforce these constraints.

[batfish-bot]

This change is 

[anothermattbrown]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ratulm)

[codecov]

Codecov Report

Merging #6422 (9f860eb) into master (5573429) will decrease coverage by 0.00%.
The diff coverage is 76.47%.

@@             Coverage Diff              @@
##             master    #6422      +/-   ##
============================================
- Coverage     73.10%   73.09%   -0.01%     
+ Complexity    35303    35296       -7     
============================================
  Files          2819     2819              
  Lines        142927   142937      +10     
  Branches      17209    17212       +3     
============================================
- Hits         104490   104485       -5     
- Misses        30174    30182       +8     
- Partials       8263     8270       +7     

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/org/batfish/common/bdd/BDDPacket.java	59.89% <76.47%> (+1.75%)	41.00 <5.00> (+1.00)
.../org/batfish/dataplane/rib/RouteAdvertisement.java	83.67% <0.00%> (-4.09%)	18.00% <0.00%> (-1.00%)
...rc/main/java/org/batfish/datamodel/flow/Trace.java	80.64% <0.00%> (-3.23%)	13.00% <0.00%> (-1.00%)
...col/src/main/java/org/batfish/role/InferRoles.java	89.54% <0.00%> (-1.37%)	50.00% <0.00%> (-1.00%)
...src/main/java/org/batfish/coordinator/PoolMgr.java	59.52% <0.00%> (-1.20%)	15.00% <0.00%> (-1.00%)
...java/org/batfish/dataplane/ibdp/VirtualRouter.java	90.54% <0.00%> (-0.34%)	208.00% <0.00%> (-1.00%)
...src/main/java/org/batfish/coordinator/WorkMgr.java	75.91% <0.00%> (-0.16%)	246.00% <0.00%> (-1.00%)
...tfish/representation/cisco/CiscoConfiguration.java	85.95% <0.00%> (-0.14%)	494.00% <0.00%> (-1.00%)