Fix CDPMsgIPPrefix in contrib.cdp when length is more than one IP address

[itform-fr]

if the length of IP addresses prefixes was more than one address all the following content wasn't interpreted (Raw payload). This change seams to fix it

Here the capture with multiple addresses in the CDPIPPrefix

Here the cdp.py dissector before modification with the pcap showed before

Here the cdp.py dissector after modification with the same pcap

That's my first participation, hope it can help

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.63%. Comparing base (8e08cbf) to head (0ce7d2d).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/contrib/cdp.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4585   +/-   ##
=======================================
  Coverage   81.62%   81.63%           
=======================================
  Files         358      358           
  Lines       85652    85656    +4     
=======================================
+ Hits        69915    69922    +7     
+ Misses      15737    15734    -3     

Files with missing lines	Coverage Δ
scapy/contrib/cdp.py	94.90% <75.00%> (-0.53%)	⬇️

... and 4 files with indirect coverage changes

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[gpotter2]

Thanks for the PR ! Looks good

[itform-fr]

Thank you for all the great work with this awesome project.