[Appveyor] Add Npcap installer

[gpotter2]

@guedou @p-l-
So apparently the npcap team suddenly decided to discontinue the chocolatey installer...
Here's a custom one.

[codecov-io]

Codecov Report

Merging #667 into master will increase coverage by 1.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #667      +/-   ##
==========================================
+ Coverage    76.7%   77.78%   +1.07%     
==========================================
  Files         125      128       +3     
  Lines       30184    31304    +1120     
==========================================
+ Hits        23152    24349    +1197     
+ Misses       7032     6955      -77

Impacted Files	Coverage Δ
scapy/arch/windows/compatibility.py	77.59% <0%> (ø)
scapy/arch/winpcapy.py	94.61% <0%> (ø)
scapy/arch/windows/__init__.py	75.46% <0%> (ø)
scapy/layers/inet6.py	78.01% <0%> (+0.16%)	⬆️
scapy/layers/inet.py	70.78% <0%> (+0.26%)	⬆️
scapy/layers/l2.py	86.05% <0%> (+0.59%)	⬆️
scapy/modules/nmap.py	71.42% <0%> (+0.75%)	⬆️
scapy/utils6.py	84.53% <0%> (+1.03%)	⬆️
scapy/utils.py	76.81% <0%> (+1.13%)	⬆️
scapy/automaton.py	80.95% <0%> (+2.91%)	⬆️
... and 8 more

[p-l-]

Thanks @gpotter2!

[guedou]

@gpotter2 Thanks ! You're awesome.