Tolerate decoding errors in LLMNR queries/responses

Fixes:
```
  File "scapy/sendrecv.py", line 1439, in tshark
  File "scapy/sendrecv.py", line 1311, in sniff
  File "scapy/sendrecv.py", line 1254, in _run
  File "scapy/sessions.py", line 109, in on_packet_received
  File "scapy/sendrecv.py", line 1436, in _cb
  File "scapy/packet.py", line 1645, in summary
  File "scapy/packet.py", line 1619, in _do_summary
  File "scapy/packet.py", line 1619, in _do_summary
  File "scapy/packet.py", line 1619, in _do_summary
  File "scapy/packet.py", line 1622, in _do_summary
  File "scapy/layers/llmnr.py", line 63, in mysummary
    self.qd.qname.decode(),
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 2: invalid start byte
```

It's a follow-up to dd7a5c9

scapy/layers/llmnr.py

@@ -55,12 +55,12 @@ def hashret(self):
     def mysummary(self):
         if self.an:
             return "LLMNRResponse '%s' is at '%s'" % (
-                self.an.rrname.decode(),
+                self.an.rrname.decode(errors="backslashreplace"),
                 self.an.rdata,
             ), [UDP]
         if self.qd:
             return "LLMNRQuery who has '%s'" % (
-                self.qd.qname.decode(),
+                self.qd.qname.decode(errors="backslashreplace"),
             ), [UDP]
 
 

test/scapy/layers/llmnr.uts

@@ -36,3 +36,9 @@ b = Ether(b'\x14\x0cv\x8f\xfe(\xd0P\x99V\xdd\xf9\x08\x00E\x00\x00(\x00\x01\x00\x
 assert b.answers(a)
 assert not a.answers(b)
 
+= Summary
+q = LLMNRQuery(b'Yy\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x01\xff\x00\x00\x01\x00\x01')
+assert q.mysummary()[0] == r"LLMNRQuery who has '\xff.'"
+
+r = LLMNRResponse(b'\n\xe6\x80\x00\x00\x01\x00\x01\x00\x00\x00\x00\x01\xff\x00\x00\x1c\x00\x01\xc0\x0c\x00\x1c\x00\x01\x00\x00\x00\x1e\x00\x10\xfe\x80\x00\x00\x00\x00\x00\x00xu\x17\xff\xfe\xbc\xac\xcb')
+assert r.mysummary()[0] == r"LLMNRResponse '\xff.' is at 'fe80::7875:17ff:febc:accb'"