21_network: Change hwclock-call from --UTC to implicit

Using --UTC is not consistent with other uses of hwclock in the scripts, resulting in the RTC to shift one or more hours every reboot. Calling hwclock with --UTC would only be correct if there were a write-call with explicit --UTC, otherwise it's best to omit it.

Have a look at the 90clock-script in /user/lib/pm-utils/sleep.d: All read- and write-calls to hwclock are implicit without either --UTC or --localtime.