network: adjust log message about DNR

The only possible error return in this position is -ENODATA, which is
not interesting.

src/network/networkd-state-file.c

@@ -601,11 +601,11 @@ static void serialize_resolvers(
 
                 r = sd_dhcp_lease_get_dnr(lease, &resolvers);
                 if (r < 0)
-                        return (void) log_warning_errno(r, "Failed to get DNR from DHCP lease, ignoring.");
+                        return (void) log_debug_errno(r, "Failed to get DNR from DHCP lease, ignoring: %m");
 
                 r = dns_resolvers_to_dot_strv(resolvers, r, &names);
                 if (r < 0)
-                        return (void) log_warning_errno(r, "Failed to get DoT servers from DHCP DNR, ignoring.");
+                        return (void) log_warning_errno(r, "Failed to get DoT servers from DHCP DNR, ignoring: %m");
                 if (r > 0)
                         fputstrv(f, names, NULL, space);
         }
@@ -617,11 +617,11 @@ static void serialize_resolvers(
 
                 r = sd_dhcp6_lease_get_dnr(lease6, &resolvers);
                 if (r < 0)
-                        return (void) log_warning_errno(r, "Failed to get DNR from DHCPv6 lease, ignoring.");
+                        return (void) log_debug_errno(r, "Failed to get DNR from DHCPv6 lease, ignoring: %m");
 
                 r = dns_resolvers_to_dot_strv(resolvers, r, &names);
                 if (r < 0)
-                        return (void) log_warning_errno(r, "Failed to get DoT servers from DHCPv6 DNR, ignoring.");
+                        return (void) log_warning_errno(r, "Failed to get DoT servers from DHCPv6 DNR, ignoring: %m");
                 if (r > 0)
                         fputstrv(f, names, NULL, space);
         }