Add javadoc for Network#netId

Bug: 151156820
Test: m doc-comment-check-docs

Change-Id: I18e6022c7b0b8bf132069f33d916d1b16d53d4f0
Merged-In: Iea34a5c58a8b77c83258a39a8a44601e21a482f5
(cherry picked from commit ab23c0fef8c02a9d63b1b48628eb687f589aac72)
1 file changed