modem-helpers: fix warnings with -Wswitch-enum

mm-modem-helpers.c: In function ‘mm_3gpp_get_pdp_type_from_ip_family’:
  mm-modem-helpers.c:4166:5: error: enumeration value ‘MM_BEARER_IP_FAMILY_NONE’ not handled in switch [-Werror=switch-enum]
   4166 |     switch (family) {
        |     ^~~~~~
  mm-modem-helpers.c:4166:5: error: enumeration value ‘MM_BEARER_IP_FAMILY_ANY’ not handled in switch [-Werror=switch-enum]

src/mm-modem-helpers.c

@@ -4170,6 +4170,8 @@ mm_3gpp_get_pdp_type_from_ip_family (MMBearerIpFamily family)
         return "IPV6";
     case MM_BEARER_IP_FAMILY_IPV4V6:
         return "IPV4V6";
+    case MM_BEARER_IP_FAMILY_NONE:
+    case MM_BEARER_IP_FAMILY_ANY:
     default:
         return NULL;
     }