Fix compilation of generated MOD file for NEURON

[iomaganaris]

• Added missing ; in instantiation of slist/dlist
• Use a variable name for the channel info array that doesn't clash with other NEURON declarations
• Fix use of mech_type variable in NEURON code

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (2c4c8e2) 88.18% compared to head (959d32c) 88.18%.

Files	Patch %	Lines
src/codegen/codegen_neuron_cpp_visitor.cpp	66.66%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1101   +/-   ##
=======================================
  Coverage   88.18%   88.18%           
=======================================
  Files         175      175           
  Lines       12903    12905    +2     
=======================================
+ Hits        11378    11380    +2     
  Misses       1525     1525           

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[bbpbuildbot]

Logfiles from GitLab pipeline #176019 (:white_check_mark:) have been uploaded here!

Status and direct links:

• ✅ spack_setup
• ✅ build:intel
• ✅ build:nvhpc
• ✅ test:intel
• ✅ test:nvhpc