Properly set the NetworkRequest singleUid.

A job's NetworkRequest should have the source app's UID as the UID. The
previous code attempted to set the UID, but didn't modify the stored
job, leading to potentially unexpected behavior of proxied jobs.
Rearranging code to ensure we properly set the NetworkRequest UID.

Bug: 311727153
Test: N/A
Change-Id: I8fb49b74ff861ea82d89ab8d2791e4b917fd6ef2