Do not abuse the IMSG_CTL_SEND_REQUEST imsg to transition to

Do not abuse the IMSG_CTL_SEND_REQUEST imsg to transition to
REBOOTING. There will be a few more cases internal to dhcpleased that
have nothing to do with the control socket.
While here move requesting a new lease via a call to dhclient under
ifndef SMALL, nothing on the ramdisk uses this.