Fix arping() when route is missing

[gpotter2]

• minor fix of the arping() function to work when routes are missing

[codecov]

Codecov Report

Attention: Patch coverage is 41.66667% with 7 lines in your changes missing coverage. Please review.

Project coverage is 81.60%. Comparing base (6f0faf3) to head (34e4085).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/layers/l2.py	41.66%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4567      +/-   ##
==========================================
- Coverage   81.61%   81.60%   -0.02%     
==========================================
  Files         356      356              
  Lines       85545    85555      +10     
==========================================
- Hits        69819    69814       -5     
- Misses      15726    15741      +15     

Files with missing lines	Coverage Δ
scapy/layers/l2.py	83.88% <41.66%> (-1.07%)	⬇️

... and 7 files with indirect coverage changes