[PATCH 5.9 005/152] ipv4: use IS_ENABLED instead of ifdef

[Greg Kroah-Hartman]

From: Florian Klink <flo...@flokli.de>

commit c09c8a27b9baa417864b9adc3228b10ae5eeec93 upstream.

Checking for ifdef CONFIG_x fails if CONFIG_x=m.

Use IS_ENABLED instead, which is true for both built-ins and modules.

Otherwise, a
> ip -4 route add 1.2.3.4/32 via inet6 fe80::2 dev eth1
fails with the message "Error: IPv6 support not enabled in kernel." if
CONFIG_IPV6 is `m`.

In the spirit of b8127113d01e53adba15b41aefd37b90ed83d631.

Fixes: d15662682db2 ("ipv4: Allow ipv6 gateway with ipv4 routes")
Cc: Kim Phillips <kim.phill...@arm.com>
Signed-off-by: Florian Klink <flo...@flokli.de>
Reviewed-by: David Ahern <dsah...@kernel.org>
Link: https://lore.kernel.org/r/20201115224509.2020651-1-flo...@flokli.de
Signed-off-by: Jakub Kicinski <k...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 net/ipv4/fib_frontend.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -696,7 +696,7 @@ int fib_gw_from_via(struct fib_config *c
                cfg->fc_gw4 = *((__be32 *)via->rtvia_addr);
                break;
        case AF_INET6:
-#ifdef CONFIG_IPV6
+#if IS_ENABLED(CONFIG_IPV6)
                if (alen != sizeof(struct in6_addr)) {
                        NL_SET_ERR_MSG(extack, "Invalid IPv6 address in 
RTA_VIA");
                        return -EINVAL;