datapath: do not use vport type to determine presence of Geneve attributes

This patch fixes following kernel crash that could happen, if geneve
vport was not added yet, but revalidator thread attempted to dump flows.
To reproduce:
1. switch tunnel type between geneve and gre in a loop; and
2. run ping.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000048
IP: [<ffffffffa0385470>] ovs_nla_put_flow+0x3d0/0x7c0 [openvswitch]
PGD 3b32b067 PUD 3b2ef067 PMD 0
Oops: 0000 [#2] SMP
...
CPU: 0 PID: 6450 Comm: revalidator2 Tainted: GF     D    O
3.13.0-24-generic #46-Ubuntu
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference
Platform, BIOS 6.00 07/02/2012
task: ffff88003b4aafe0 ti: ffff88003d314000 task.ti: ffff88003d314000
RIP: 0010:[<ffffffffa0385470>]  [<ffffffffa0385470>]
ovs_nla_put_flow+0x3d0/0x7c0 [openvswitch]
RSP: 0018:ffff88003d315a10  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88003a9a9960 RCX: 0000000000000000
RDX: 0000000000000002 RSI: ffffffffffffffc8 RDI: ffff88003babcb80
RBP: ffff88003d315a68 R08: 0000000000000000 R09: 0000000000000004
R10: ffff880039c23034 R11: 0000000000000008 R12: ffff88003a861600
R13: ffff88003a9a9960 R14: ffff88003babcb80 R15: qffff88003a861600
FS:  00007ff0f5d94700(0000) GS:ffff88003f600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000048 CR3: 000000003b55b000 CR4: 00000000000007f0
Stack:
ffffffff81385093 0000000000000000 0000000000000000 0000000000000000
ffff880000000000 ffff88003d315a58 ffff880039c23014 ffff88003a9a97a0
ffff88003babcb80 ffff880039c23018 ffff88003a861600 ffff88003d315ad0
Call Trace:
[<ffffffff81385093>] ? __nla_reserve+0x43/0x50
[<ffffffffa037e683>] ovs_flow_cmd_fill_info+0x93/0x2b0 [openvswitch]
[<ffffffffa0387159>] ? ovs_flow_tbl_dump_next+0x49/0xc0 [openvswitch]
[<ffffffffa037e920>] ovs_flow_cmd_dump+0x80/0xd0 [openvswitch]
[<ffffffff81645004>] netlink_dump+0x84/0x240
[<ffffffff816458eb>] __netlink_dump_start+0x1ab/0x220
[<ffffffff816498d7>] genl_family_rcv_msg+0x337/0x370
[<ffffffffa037e8a0>] ? ovs_flow_cmd_fill_info+0x2b0/0x2b0 [openvswitch]
[<ffffffff811a2778>] ? __kmalloc_node_track_caller+0x58/0x1e0
[<ffffffff81649910>] ? genl_family_rcv_msg+0x370/0x370
[<ffffffff816499a1>] genl_rcv_msg+0x91/0xd0
[<ffffffff81647a29>] netlink_rcv_skb+0xa9/0xc0
[<ffffffff81647f28>] genl_rcv+0x28/0x40
[<ffffffff81647055>] netlink_unicast+0xd5/0x1b0
[<ffffffff8164742f>] netlink_sendmsg+0x2ff/0x740
[<ffffffff816024eb>] sock_sendmsg+0x8b/0xc0
[<ffffffff811bbaa1>] ? __sb_end_write+0x31/0x60
[<ffffffff811d42bf>] ? touch_atime+0x10f/0x140
[<ffffffff811c2471>] ? pipe_read+0x371/0x400
[<ffffffff81602691>] SYSC_sendto+0x121/0x1c0
[<ffffffff8109dd84>] ? vtime_account_user+0x54/0x60
[<ffffffff81020d35>] ? syscall_trace_enter+0x145/0x250
[<ffffffff8160319e>] SyS_sendto+0xe/0x10
[<ffffffff8172663f>] tracesys+0xe1/0xe6

Signed-Off-By: Ansis Atteka <aatteka@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>