lib: net_utils: enforce '.' as octet separator in string_to_ip

Ensure '.' is used to separate octets. If another character is seen
reject the string outright and return 0.0.0.0.

Signed-off-by: Chris Packham <judge.packham@gmail.com>

lib/net_utils.c

@@ -28,6 +28,10 @@ struct in_addr string_to_ip(const char *s)
 			addr.s_addr = 0;
 			return addr;
 		}
+		if (i != 3 && *e != '.') {
+			addr.s_addr = 0;
+			return addr;
+		}
 		addr.s_addr <<= 8;
 		addr.s_addr |= (val & 0xFF);
 		if (s) {