datapath: backport: ovs: align nlattr properly when needed

datapath: backport: ovs: align nlattr properly when needed

Upstream commit:
    commit 66c7a5ee1a6b7c69d41dfd68d207fdd54efba56a
    Author: Nicolas Dichtel <nicolas.dichtel@6wind.com>

    ovs: align nlattr properly when needed

    I also fix commit 8b32ab9e6ef1: use nla_total_size_64bit() for
    OVS_FLOW_ATTR_USED in ovs_flow_cmd_msg_size().

    Fixes: 8b32ab9e6ef1 ("ovs: use nla_put_u64_64bit()")
    Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Jesse Gross <jesse@kernel.org>