net: reallocate new socket option number for IPV6_AUTOFLOWLABEL

cb1ce2ef ("ipv6: Implement automatic flow label generation on transmit")
accidentally uses socket option 64, which is already used by ip6tables:

 IP6T_SO_SET_REPLACE / IP6T_SO_GET_INFO               64
 IP6T_SO_SET_ADD_COUNTERS / IP6T_SO_GET_ENTRIES       65

There is comment include/uapi/linux/in6.h warning about that.

Allocate 70 for this, which seems to be unused instead.

Cc: Tom Herbert <therbert@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/in6.h

@@ -233,7 +233,6 @@ struct in6_flowlabel_req {
 #if 0	/* not yet */
 #define IPV6_USE_MIN_MTU	63
 #endif
-#define IPV6_AUTOFLOWLABEL	64
 
 /*
  * Netfilter (1)
@@ -262,6 +261,7 @@ struct in6_flowlabel_req {
  * IP6T_SO_ORIGINAL_DST		80
  */
 
+#define IPV6_AUTOFLOWLABEL	70
 /* RFC5014: Source address selection */
 #define IPV6_ADDR_PREFERENCES	72