DHCP ciaddr unable to set to 0 for DHCPDECLINE

[soxrok2212]

According to RFC 2131 page 36, DHCP ciaddr should be set to the client's MAC address in the case of a DHCPRELEASE message. However, for a DHCPDECLINE, it should be set to 0. However, the parser requires it be set to an IP address.

https://github.com/tomac/yersinia/blob/master/src/dhcp.h#L269-L270

[soxrok2212]

This can be reproduced on the CLI with the -ci arg, e.g.
yersinia dhcp -source xx:xx:xx:xx:xx:xx -interface eth0 -attack 0 -dest yy:yy:yy:yy:yy:yy -htype 1 -hlen 6 -hops 0 -xid 12345678 -ch xx:xx:xx:xx:xx:xx -ci 0