net: add doc for in6_pton()

It is not easy to use in6_pton() correctly without reading
its definition, so add some doc for it.

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/utils.c

@@ -161,6 +161,18 @@ out:
 }
 EXPORT_SYMBOL(in4_pton);
 
+/**
+ * in6_pton - convert an IPv6 address from literal to binary representation
+ * @src: the start of the IPv6 address string
+ * @srclen: the length of the string, -1 means strlen(src)
+ * @dst: the binary (u8[16] array) representation of the IPv6 address
+ * @delim: the delimiter of the IPv6 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 in6_pton(const char *src, int srclen,
 	     u8 *dst,
 	     int delim, const char **end)