Use user-defined data limits in multipath quota.

When data plan information is not available, use user-defined data
warning or limit to estimate a reasonable multipath quota.

New version of change to avoid editing NetworkPolicyManagerService.

Test: Tests in go/ag/3828171 pass.
Bug: 72631572
Bug: 72877610
Change-Id: Ied4215a093377dc3322c4f18a83969d364c19b2a