[tor-bugs] #9354 [Tor]: NumDirectoryGuards should track NumEntryGuards

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#9354: NumDirectoryGuards should track NumEntryGuards
------------------------+---------------------------------------------------
 Reporter:  arma        |          Owner:                    
     Type:  defect      |         Status:  new               
 Priority:  normal      |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor         |        Version:                    
 Keywords:  tor-client  |         Parent:                    
   Points:              |   Actualpoints:                    
------------------------+---------------------------------------------------
 If you change NumEntryGuards to 1, your Tor will still contact 3 relays
 for directory information, since you didn't realize you had to set
 NumDirectoryGuards too. This fails the 'no surprises' principle.

 At the same time, we have this check:
 {{{
   if (options->UseEntryGuards && ! options->NumEntryGuards)
     REJECT("Cannot enable UseEntryGuards with NumEntryGuards set to 0");
 }}}
 but no corresponding check for "UseEntryGuardsAsDirGuards 1 but
 NumDirectoryGuards 0".

 I think the right behavior should be to treat NumDirectoryGuards 0 as "use
 the value from numentryguards", and change that to the default.

 Bug encountered by Isis.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9354>
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