inet_addr: return INADDR_NONE(-1) when input string is invalid

now:
inet_network("300.10.10.10"); return 0
inet_addr("300.10.10.10"); return 0

glibc and muscle both return INADDR_NONE or -1.

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

libs/libc/net/lib_inetaddr.c

@@ -88,7 +88,7 @@ in_addr_t inet_addr(FAR const char *cp)
   unsigned int b;
   unsigned int c;
   unsigned int d;
-  uint32_t result = 0;
+  uint32_t result = INADDR_NONE;
 
   switch (sscanf(cp, "%u.%u.%u.%u", &a, &b, &c, &d))
     {