[NETFILTER]: nfnetlink_log: zero-terminate prefix

Userspace expects a zero-terminated string, so include the trailing
zero in the netlink message.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/nfnetlink_log.c

@@ -615,7 +615,7 @@ nfulnl_log_packet(unsigned int pf,
 
 	plen = 0;
 	if (prefix)
-		plen = strlen(prefix);
+		plen = strlen(prefix) + 1;
 
 	/* all macros expand to constant values at compile time */
 	/* FIXME: do we want to make the size calculation conditional based on