Issue #166 Fix.

[seamustuohy]

Made single adhoc interface condition explicit about requirement for a "single" adhoc interface. It had been falling back to a state that assumed at least one ad-hoc interface existed without asserting it.

per: #166
@areynold

To test this pull request.

• Create a build with this branch of luci-commotion
• Configure node though setup wizard
• Go to the menu Basic Configuration --> Mesh Network
• Click on the delete button of the mesh interface
• Click save
• Apply the changes
• Go to Security --> Passwords
• If the interface errors out this patch did not work.