AnsweringMachines: better defaults, various fixes, more tests

[gpotter2]

This PR:

• restores using sendp instead of send in AnsweringMachines. This works better in some cases (e.g. ICMP)
• Test some answering machines that were yet untested (LdapPing_am)
• Cleanup the NBNS answering machine and regroup with LdapPing_am
• fixes Fix ICMPEcho_am description #4051

[codecov]

Codecov Report

Attention: Patch coverage is 90.38462% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 82.17%. Comparing base (cd2fed9) to head (744e727).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4358      +/-   ##
==========================================
+ Coverage   82.13%   82.17%   +0.04%     
==========================================
  Files         350      350              
  Lines       83136    83155      +19     
==========================================
+ Hits        68280    68334      +54     
+ Misses      14856    14821      -35     

Files	Coverage Δ
scapy/ansmachine.py	67.93% <100.00%> (ø)
scapy/layers/dhcp.py	83.49% <100.00%> (-0.06%)	⬇️
scapy/layers/dhcp6.py	86.08% <100.00%> (+0.19%)	⬆️
scapy/layers/dot11.py	91.40% <100.00%> (ø)
scapy/layers/inet.py	71.69% <100.00%> (+0.06%)	⬆️
scapy/layers/netbios.py	92.42% <100.00%> (+7.28%)	⬆️
scapy/layers/dns.py	88.72% <84.61%> (+1.10%)	⬆️
scapy/layers/ldap.py	58.81% <86.95%> (+4.96%)	⬆️

... and 4 files with indirect coverage changes

[polybassa]

Nice PR, LGTM