Remove the support for NGM_CISCO_GET_IPADDR message from ng_iface(4). The
legitimacy of removal is proved by the fact that implementation contained
a critical bug: the response allocated was sizeof(pointer), while should
had been 2*sizeof(struct ng_cisco_ipaddr). The reason for ng_iface(4) to
support ng_cisco(4) message isn't explained anywhere, and code comes from
original Whistle import.

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