#213 opendmark leaks resources on NetBSD

[Roy Marples]

On NetBSD at least, if nres_init is called resources should be freed with nres_destroy as nres_close is not enough. The symptom is that the system runs out of file descriptors quite quickly.

[Roy Marples]

Path to correct issue.
Also detects nres_init correctly has those functions are namespace protected.

[Juri Haberland]

Using this patch on Ubuntu 16.04 produces the following warning:

opendmarc_dns.c: In function ‘dmarc_dns_get_record’:
opendmarc_dns.c:210:50: warning: passing argument 2 of ‘opendmarc_policy_library_dns_hook’ from incompatible pointer type [-Wincompatible-pointer-types]
                                                  &resp.nsaddr_list);
                                                  ^
In file included from opendmarc_dns.c:15:0:
opendmarc_internal.h:233:6: note: expected ‘struct sockaddr_in *’ but argument is of type ‘struct sockaddr_in (*)[3]’
 void opendmarc_policy_library_dns_hook(int *nscountp, struct sockaddr_in *nsaddr_list);
      ^

[Roy Marples]

I'd rather live with compile warnings than leak resources.
Without this patch my mail server runs out of resources in a few hours use.

Besides, on NetBSD there are a load of compile warnings as it stands without this patch.