Add a switch to disable SNMP support.

[piste-jp]

Summary: Add a switch to disable SNMP support

Description

Add a switch to disable SNMP support because it can't be supported under OSX (macOS) Homebrew environment. --disable-snmp is needed to build on OSX (macOS) Homebrew environment.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have confirmed my fix is effective or that my feature works