conf.route: improve doc

[gpotter2]

• add some doc in conf.route
• minor doc fixes

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 49.09%. Comparing base (892b738) to head (b1804bd).

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4399       +/-   ##
===========================================
- Coverage   81.48%   49.09%   -32.40%     
===========================================
  Files         352      345        -7     
  Lines       83995    78150     -5845     
===========================================
- Hits        68443    38366    -30077     
- Misses      15552    39784    +24232     

Files	Coverage Δ
scapy/route.py	22.55% <0.00%> (-67.75%)	:arrow_down:

... and 265 files with indirect coverage changes