Use parallel DNS resolution for PLMN-based FQDNs

- Useful for RJIO IN carrier, which has 22 carrier config PLMNs.
- Preserves sorted order of domain names / IP address results.
- No functional difference from existing method.

Bug: 229015525
Test: Live tests on TMO and RJIO PLMNs. EpdgSelectorTests pass.
Change-Id: Ia109df891932a536272b9708b11f381da2cf1d06
1 file changed