mlx4_core: Get rid of redundant ext_port_cap flags

While doing the work for commit a6f7feae ("IB/mlx4: pass SMP
vendor-specific attribute MADs to firmware") we realized that the
firmware would respond on all sorts of vendor-specific MADs.
Therefore commit 97285b78 ("mlx4_core: Add extended port
capabilities support") adds redundant code into the driver, since
there's no real reaon to maintain the extended capabilities of the
port, as they can be queried on demand (e.g the FDR10 capability).

This patch reverts commit 97285b78 and removes the check for
extended caps from the mlx4_ib driver port query flow.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>