RDMA: Verify port when creating flow rule

Validate port value provided by the user and with that remove no longer
needed validation by the driver.  The missing check in the mlx5_ib driver
could cause to the below oops.

Call trace:
  _create_flow_rule+0x2d4/0xf28 [mlx5_ib]
  mlx5_ib_create_flow+0x2d0/0x5b0 [mlx5_ib]
  ib_uverbs_ex_create_flow+0x4cc/0x624 [ib_uverbs]
  ib_uverbs_handler_UVERBS_METHOD_INVOKE_WRITE+0xd4/0x150 [ib_uverbs]
  ib_uverbs_cmd_verbs.isra.7+0xb28/0xc50 [ib_uverbs]
  ib_uverbs_ioctl+0x158/0x1d0 [ib_uverbs]
  do_vfs_ioctl+0xd0/0xaf0
  ksys_ioctl+0x84/0xb4
  __arm64_sys_ioctl+0x28/0xc4
  el0_svc_common.constprop.3+0xa4/0x254
  el0_svc_handler+0x84/0xa0
  el0_svc+0x10/0x26c
 Code: b9401260 f9615681 51000400 8b001c20 (f9403c1a)

Fixes: 436f2ad0

 ("IB/core: Export ib_create/destroy_flow through uverbs")
Link: https://lore.kernel.org/r/faad30dc5219a01727f47db3dc2f029d07c82c00.1623309971.git.leonro@nvidia.com
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>