Don't use the "tun" interface prefix for resolvconf call

[Zensey]

The symptoms:
MystDark / node consumer doesn't work on Linux.
MystDark operates the node using --usermode flag.

But on establishing connection node (usermode) calls myst_superviser to do wg-up, which results into command:

script_type=up dev=myst0 foreign_option_1="dhcp-option DNS 10.182.3.1" /home/user/src/node/build/myst/config/update-resolv-conf

and it fails with

Failed to resolve interface "tun.myst0": No such device

The problem might not have been noticed if testing was carried out in VM / headless Linux, as it lacks resolvconf.
The problem only appears when OS has resolvconf.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d99042a) 37.78% compared to head (4e98ea3) 37.83%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5979      +/-   ##
==========================================
+ Coverage   37.78%   37.83%   +0.05%     
==========================================
  Files         371      371              
  Lines       20665    20665              
==========================================
+ Hits         7808     7819      +11     
+ Misses      12075    12065      -10     
+ Partials      782      781       -1     

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