dhclient - Remove cur_time global.

dhclient - Remove cur_time global.

- Junk global cur_time, and use time(NULL) or local variables where
  time is checked multiple times. Add a set_timeout_interval() function
  to allow setting a timeout based on an interval from current time.

- Fixes issues with initial startup where the global cur_time was
  always old and caused initial DHCPDISCOVER or DHCPREQUEST packets
  to be sent multiple times. And probably other timeout related
  oddities.

Taken-from: OpenBSD