[MS27] Expose noteUntaggedSocket SystemApi

While Data usage related codes are moving to mainline module,
StrictMode#vmUntaggedSocketEnabled() and onUntaggedSocket()
can no longer be accessed from NetworkManagementSocketTagger.

Thus, expose alternative SystemApi to allow invocations from
the module.

Test: TH
Bug: 204830222
Exempt-From-Owner-Approval: 1. Owner approved the change with
  explicitly granted submission after adderessing the
  straight-forward comment. 2. Owner is OOO for 3 months.
Change-Id: Ib54ff54ce3617ae0d04080a1740e78b086bbb039