Add mDNS daemon

[gpotter2]

• add new mdnsd (mDNS_am) command
• add tests for mDNS_am
• also add tests for LLMNR_am

[codecov]

Codecov Report

Attention: Patch coverage is 72.41379% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 82.20%. Comparing base (29b5413) to head (a6c3e58).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4385      +/-   ##
==========================================
+ Coverage   81.56%   82.20%   +0.63%     
==========================================
  Files         352      352              
  Lines       83601    83622      +21     
==========================================
+ Hits        68193    68743     +550     
+ Misses      15408    14879     -529     

Files	Coverage Δ
scapy/layers/llmnr.py	97.87% <ø> (ø)
scapy/layers/dns.py	88.26% <72.41%> (-0.37%)	⬇️

... and 18 files with indirect coverage changes

[evverx]

Looks like it doesn't work with avahi-resolve -n. When that command is run without -4 or -6 avahi sends A and AAAA queries and since only A can be answered no replies are sent by scapy. I "fixed" it with

diff --git a/scapy/layers/dns.py b/scapy/layers/dns.py
index c1977429..80902dcf 100644
--- a/scapy/layers/dns.py
+++ b/scapy/layers/dns.py
@@ -1649,8 +1649,6 @@ class DNS_am(AnsweringMachine):
                         continue  # next
                 except TimeoutError:
                     pass
-            # Error
-            break
         else:
             if not ans:
                 # No rq was actually answered, as none was valid. Discard.

but there should probably be a better way to fix that closer to the rq.qtype in [1, 28] clause. I'll try to come up with a better fix.

[gpotter2]

Thanks for looking into this.

I've played around with it quite a bit and there are numerous other inconsistencies compared to a normal server. The IP id is wrong, same for the ttl, etc. I'll PR some changes tonight.