[VCN02] Make LingerTimer takes request Id instead of NetworkRequest

Currently, LingerTimer takes a NetworkRequest for internal use.
However, this is unnecessary since only request Id is used.

Thus, this patch allows subsequent patches to remove the need
of a NetworkRequest when creating a LingerTimer. And the output
of lingered requests is reduced to id instead of printing
content of requests.

Test: atest FrameworksNetTests
Bug: 175180558
Change-Id: I9106d0804f1083942e1fcaca842f547c0aee1840