libpcap: make L3socket send() follow routing

[gpotter2]

This makes the L3pcapSocket behave similarly to the other L3*Socket(s).

In a L3 socket, the destination is used to chose the interface to send the packet on. This means that Scapy should be able to created another pcap file descriptor if the currently bound one isn't on the proper interface.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 11.53846% with 23 lines in your changes are missing coverage. Please review.

Project coverage is 49.08%. Comparing base (892b738) to head (adbb832).

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4398       +/-   ##
===========================================
- Coverage   81.48%   49.08%   -32.41%     
===========================================
  Files         352      345        -7     
  Lines       83995    78170     -5825     
===========================================
- Hits        68443    38368    -30075     
- Misses      15552    39802    +24250     

Files	Coverage Δ
scapy/arch/windows/__init__.py	62.42% <50.00%> (+62.42%)	:arrow_up:
scapy/arch/libpcap.py	35.15% <8.33%> (-37.20%)	:arrow_down:

... and 264 files with indirect coverage changes