Support dhcpd min-secs (bnc#bnc889314)

This is a refresh of pullrequest #375 

Support min-secs in dhcpd.conf by always setting correct ->secs field in DHCP4 request.
Rework the timeout handling to achive this. There is now a capture timeout and a fsm timeout.
The capture timeout is based on suggestions from RFC 2131, 4.1. (4sec, expontial,up to 64secs)
The fsm timeout is based on aquire-timeout, which comes from DHCLIENT_TIMEOUT.