net: add doc for in4_pton()

It is not easy to use in4_pton() correctly without reading
its definition, so add some doc for it.

Cc: David S. Miller <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/utils.c

···
 	return IN6PTON_UNKNOWN;
 }
 
+/**
+ * in4_pton - convert an IPv4 address from literal to binary representation
+ * @src: the start of the IPv4 address string
+ * @srclen: the length of the string, -1 means strlen(src)
+ * @dst: the binary (u8[4] array) representation of the IPv4 address
+ * @delim: the delimiter of the IPv4 address in @src, -1 means no delimiter
+ * @end: A pointer to the end of the parsed string will be placed here
+ *
+ * Return one on success, return zero when any error occurs
+ * and @end will point to the end of the parsed string.
+ *
+ */
 int in4_pton(const char *src, int srclen,
 	     u8 *dst,
 	     int delim, const char **end)