MINOR: dns: Dynamically allocate dns options to reduce the act_rule size

<.arg.dns.dns_opts> field in the act_rule structure is now dynamically allocated
when a do-resolve rule is parsed. This drastically reduces the structure size.
diff --git a/include/types/action.h b/include/types/action.h
index 6ec3f01..293e1d8 100644
--- a/include/types/action.h
+++ b/include/types/action.h
@@ -115,7 +115,7 @@
 			char *varname;
 			char *resolvers_id;
 			struct dns_resolvers *resolvers;
-			struct dns_options dns_opts;
+			struct dns_options *dns_opts;
 		} dns;                         /* dns resolution */
 		struct {
 			int i;                 /* integer param (status, nice, loglevel, ..) */