fix license register error in airgap mode

[anjalshireesh]

Description

A network lookup was happening even in airgap mode, resulting in failure of the command.

Motivation and Context

Bugfix

How to test this PR?

• Ensure that your client machine doesn't have internet connectivity
• Run mc license register <alias> --airgap
• Verify that the command doesn't error out and prints the subnet url to be visited for registration

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (PR Do not allow registration of play cluster #4647)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here