Update networkmanager.md

[schraf]

Class name is UNetTransport

Select the type of change:

• Small Changes - Typos, formatting, slight revisions
• New Content - New features, sections, pages, tutorials
• Site and Tools - Updates, maintenance, and new packages for the site and Docusaurus

Purpose of the Pull Request:

Fixes a typo from UnetTransport to UNetTransport.

Issue Number:

[lkrell]

Thanks for the catch and update!