netfilter: xt_recent: fix (increase) ipv6 literal buffer length

in6_pton() supports 'low-32-bit dot-decimal representation'
(this is useful with DNS64/NAT64 networks for example):

  # echo +aaaa:bbbb:cccc:dddd:eeee:ffff:1.2.3.4 > /proc/self/net/xt_recent/DEFAULT
  # cat /proc/self/net/xt_recent/DEFAULT
  src=aaaa:bbbb:cccc:dddd:eeee:ffff:0102:0304 ttl: 0 last_seen: 9733848829 oldest_pkt: 1 9733848829

but the provided buffer is too short:

  # echo +aaaa:bbbb:cccc:dddd:eeee:ffff:255.255.255.255 > /proc/self/net/xt_recent/DEFAULT
  -bash: echo: write error: Invalid argument

Fixes: 079aa88f ("netfilter: xt_recent: IPv6 support")
Signed-off-by: Maciej Żenczykowski <zenczykowski@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_recent.c

@@ -561,7 +561,7 @@ recent_mt_proc_write(struct file *file, const char __user *input,
 {
 	struct recent_table *t = pde_data(file_inode(file));
 	struct recent_entry *e;
-	char buf[sizeof("+b335:1d35:1e55:dead:c0de:1715:5afe:c0de")];
+	char buf[sizeof("+b335:1d35:1e55:dead:c0de:1715:255.255.255.255")];
 	const char *c = buf;
 	union nf_inet_addr addr = {};
 	u_int16_t family;