net/ipv6: set expires in modify_prefix_route() if RTF_EXPIRES is set.

Make the decision to set or clean the expires of a route based on the
RTF_EXPIRES flag, rather than the value of the "expires" argument.

This patch doesn't make difference logically, but make inet6_addr_modify()
and modify_prefix_route() consistent.

The function inet6_addr_modify() is the only caller of
modify_prefix_route(), and it passes the RTF_EXPIRES flag and an expiration
value. The RTF_EXPIRES flag is turned on or off based on the value of
valid_lft. The RTF_EXPIRES flag is turned on if valid_lft is a finite value
(not infinite, not 0xffffffff). Even if valid_lft is 0, the RTF_EXPIRES
flag remains on. The expiration value being passed is equal to the
valid_lft value if the flag is on. However, if the valid_lft value is
infinite, the expiration value becomes 0 and the RTF_EXPIRES flag is turned
off. Despite this, modify_prefix_route() decides to set the expiration
value if the received expiration value is not zero. This mixing of infinite
and zero cases creates an inconsistency.
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -4783,7 +4783,7 @@ static int modify_prefix_route(struct inet6_ifaddr *ifp,
 		table = f6i->fib6_table;
 		spin_lock_bh(&table->tb6_lock);
 
-		if (!expires) {
+		if (!(flags & RTF_EXPIRES)) {
 			fib6_clean_expires(f6i);
 			fib6_remove_gc_list(f6i);
 		} else {