Whitelist Go 1.12 for tcpip/time_unsafe.go
Whitelist Go 1.12 for tcpip/time_unsafe.go

The signature of time.now has remained unchanged:
https://github.com/golang/go/blob/c2412a7681d5beaeb5a4ceef3b2b7886361282ce/src/time/time.go#L1072

PiperOrigin-RevId: 224061160

google/netstack