Set clientId when parsing an explicit DHCP_CLIENT_IDENTIFIER option.

Bug: 130741856
Test: atest NetworkStackTests TetheringTests
Test: manually turn on the hotspot and verify the downstream device
      can attach to the upstream hotspot, then turn it off, repeat
      multiple times.
Merged-In: I9da5fec47a74de36869e795fa9b1d7170d2f91c9
Change-Id: I9da5fec47a74de36869e795fa9b1d7170d2f91c9