ipv4: add missing initialization for flowi4_uid

ipv4: add missing initialization for flowi4_uid

[ Upstream commit 8bcfd0925ef15f072ba1e7bee2c25e9e1b5fd6ca ]

Avoid matching of random stack value for uid when rules
are looked up on input route or when RP filter is used.
Problem should affect only setups that use ip rules with
uid range.

Fixes: 622ec2c9d524 ("net: core: add UID to flows, rules, and routes")
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>