Catch ServiceSpecificException instead of IllegalStateException.

The old NetworkManagementService methods to start clatd threw
IllegalStateException, but the new netd methods throw
ServiceSpecificException. Update the catch clauses so that if
starting clatd fails, the system doesn't crash.

Also stop logging stack traces but only include the exception
message itself.

Bug: 65674744
Test: atest FrameworksNetTests
Test: connecting/disconnecting to v6-only wifi in a loop does not crash
Change-Id: I4a9ec7f104712fbbe08f4f67e3288df03e8ed873