ipv6: Initialize fib6_result in bpf_ipv6_fib_lookup

fib6_result is not initialized in bpf_ipv6_fib_lookup and potentially
passses garbage to the fib lookup which triggers a KASAN warning:

[  262.055450] ==================================================================
[  262.057640] BUG: KASAN: user-memory-access in fib6_rule_suppress+0x4b/0xce
[  262.059488] Read of size 8 at addr 00000a20000000b0 by task swapper/1/0
[  262.061238]
[  262.061673] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.1.0-rc5+ #56
[  262.063493] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1 04/01/2014
[  262.065593] Call Trace:
[  262.066277]  <IRQ>
[  262.066848]  dump_stack+0x7e/0xbb
[  262.067764]  kasan_report+0x18b/0x1b5
[  262.069921]  __asan_load8+0x7f/0x81
[  262.070879]  fib6_rule_suppress+0x4b/0xce
[  262.071980]  fib_rules_lookup+0x275/0x2cd
[  262.073090]  fib6_lookup+0x119/0x218
[  262.076457]  bpf_ipv6_fib_lookup+0x39d/0x664
...

Initialize fib6_result to 0.

Fixes: b1d40991 ("ipv6: Rename fib6_multipath_select and pass fib6_result")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -4680,8 +4680,8 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 {
 	struct in6_addr *src = (struct in6_addr *) params->ipv6_src;
 	struct in6_addr *dst = (struct in6_addr *) params->ipv6_dst;
+	struct fib6_result res = {};
 	struct neighbour *neigh;
-	struct fib6_result res;
 	struct net_device *dev;
 	struct inet6_dev *idev;
 	struct flowi6 fl6;