libnm: backport symbols nm_setting_ip_config_get_dns_priority to libnm_1_2_4

Commit bdd0e7fec0 which added symbol
nm_setting_ip_config_get_dns_priority to libnm_1_4_0 was backported
to nm-1-2 in commit ad1cdcf6571da23e3197b09f1b4b14d23b8899d1.

Add the backported symbol to master to allow seemless upgrading
from 1.2.4 to 1.4.0.

libnm-core/nm-setting-ip-config.c

@@ -1700,6 +1700,7 @@ nm_setting_ip_config_get_dns_priority (NMSettingIPConfig *setting)
 
 	return NM_SETTING_IP_CONFIG_GET_PRIVATE (setting)->dns_priority;
 }
+NM_BACKPORT_SYMBOL (libnm_1_2_4, gint, nm_setting_ip_config_get_dns_priority, (NMSettingIPConfig *setting), (setting));
 
 /**
  * nm_setting_ip_config_get_num_addresses:

libnm/libnm.ver

@@ -1059,6 +1059,10 @@ global:
 	nm_vpn_service_plugin_set_login_banner;
 } libnm_1_0_0;
 
+libnm_1_2_4 {
+	#nm_setting_ip_config_get_dns_priority@libnm_1_2_4;
+} libnm_1_2_0;
+
 libnm_1_4_0 {
 global:
 	nm_device_team_get_config;