Revert "net: Use TICKS_UNLIMITED if there are no timers"

This reverts commit 5680396a.

The network timers do not trigger with this patch so this needs
to be reverted for time being.

Change-Id: If653e3ecaae1ebddabe26227af876ff6b592675b
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>