Add additional OWNERS for SNTP client code

Add additional OWNERS for SNTP client code.  This may be enough to cover
test code that will match the same patterns in
core/tests/coretests/src/android/net (which imports/includes
core/java/android/net/OWNERS). If not, there will be a follow-up for
test code.

Test: None
Bug: 199481251
Change-Id: I1dd6ce6afa0cb441279f3fad3e82483ce6dcaf1b