parse-util: introduce parse_ifindex() and make use of it everywhere

We have enough places where we parse an ifindex, hence introduce a
proper parsing function for it, that verifies all parameters.

src/libsystemd/sd-device/sd-device.c

@@ -356,13 +356,10 @@ int device_set_ifindex(sd_device *device, const char *_ifindex) {
         assert(device);
         assert(_ifindex);
 
-        r = safe_atoi(_ifindex, &ifindex);
+        r = parse_ifindex(_ifindex, &ifindex);
         if (r < 0)
                 return r;
 
-        if (ifindex <= 0)
-                return -EINVAL;
-
         r = device_add_property_internal(device, "IFINDEX", _ifindex);
         if (r < 0)
                 return r;
@@ -632,11 +629,9 @@ _public_ int sd_device_new_from_device_id(sd_device **ret, const char *id) {
                 struct ifreq ifr = {};
                 int ifindex;
 
-                r = safe_atoi(&id[1], &ifr.ifr_ifindex);
+                r = parse_ifindex(&id[1], &ifr.ifr_ifindex);
                 if (r < 0)
                         return r;
-                else if (ifr.ifr_ifindex <= 0)
-                        return -EINVAL;
 
                 sk = socket(PF_INET, SOCK_DGRAM, 0);
                 if (sk < 0)

src/libsystemd/sd-login/sd-login.c

@@ -932,9 +932,7 @@ _public_ int sd_machine_get_ifindices(const char *machine, int **ifindices) {
 
                 *(char*) (mempcpy(buf, word, l)) = 0;
 
-                if (safe_atoi(buf, &ifi) < 0)
-                        continue;
-                if (ifi <= 0)
+                if (parse_ifindex(buf, &ifi) < 0)
                         continue;
 
                 if (!GREEDY_REALLOC(ni, allocated, nr+1)) {