Fix the wifi network empty list

When checking `FocusLastSelectedView` we should use the scroll view
as the parent. Using kWIFI will create the wifi list view in the
scroll view although there's no need to.

The Ethernet section should also hold the warning messages. So type
kAll can return the entire scroll_content, which contains all type
of network lists.

Bug: b/270244573
Change-Id: I1a5c7bffc43c05cc78906cd5d1f1f93077817c72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4285398
Reviewed-by: Andre Le <leandre@chromium.org>
Commit-Queue: Jiaming Cheng <jiamingc@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1108706}