IB/mlx4: pass SMP vendor-specific attribute MADs to firmware

In the current code, vendor-specific MADs (e.g with the FDR-10
attribute) are silently dropped by the driver, resulting in timeouts
at the sending side and inability to query/configure the relevant
feature.  However, the ConnectX firmware is able to handle such MADs.
For unsupported attributes, the firmware returns a GET_RESPONSE MAD
containing an error status.

For example, for a FDR-10 node with LID 11:

    # ibstat mlx4_0 1

    CA: 'mlx4_0'
    Port 1:
    State: Active
    Physical state: LinkUp
    Rate: 40 (FDR10)
    Base lid: 11
    LMC: 0
    SM lid: 24
    Capability mask: 0x02514868
    Port GUID: 0x0002c903002e65d1
    Link layer: InfiniBand

Extended Port Query (EPI) vendor mad timeouts before the patch:

    # smpquery MEPI 11 -d

    ibwarn: [4196] smp_query_via: attr 0xff90 mod 0x0 route Lid 11
    ibwarn: [4196] _do_madrpc: retry 1 (timeout 1000 ms)
    ibwarn: [4196] _do_madrpc: retry 2 (timeout 1000 ms)
    ibwarn: [4196] _do_madrpc: timeout after 3 retries, 3000 ms
    ibwarn: [4196] mad_rpc: _do_madrpc failed; dport (Lid 11)
    smpquery: iberror: [pid 4196] main: failed: operation EPI: ext port info query failed

EPI query works OK with the patch:

    # smpquery MEPI 11 -d

    ibwarn: [6548] smp_query_via: attr 0xff90 mod 0x0 route Lid 11
    ibwarn: [6548] mad_rpc: data offs 64 sz 64
    mad data
    0000 0000 0000 0001 0000 0001 0000 0001
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    # Ext Port info: Lid 11 port 0
    StateChangeEnable:...............0x00
    LinkSpeedSupported:..............0x01
    LinkSpeedEnabled:................0x01
    LinkSpeedActive:.................0x01

Signed-off-by: Jack Morgenstein <jackm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Acked-by: Ira Weiny <weiny2@llnl.gov>
Cc: <stable@vger.kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>