dataset selects a channel from channel 11 to 24

Many Thread radio chips need to reduce their transmit power on edge
channels to pass regulatory RF certification. This CL restrcits the
dataset to select a channel from channel 11 to 24.

Bug: b/331708479
Test: atest ThreadNetworkUnitTests
Change-Id: I758c9f33629a0cafcc39bb9fde0ad45ab2699db8
2 files changed