DHCP lease time bug

[harvald]

Expected behavior:

1. Run dhcp.exe
2. Get valid configuration from server
3. Use any program from mtcp package until lease time run out.
4. Optionally get warning that lease time is running out, but continue to run until then.

Current behavior:

1. Run dhcp.exe
2. Get valid configuration from server
3. Use any program until lease time is less than 1 hour, then mtcp refuses to run.

Default lease time of some dhcp servers is one hour (i.e. dnsmasq) what might make some confusion.