RDMA: Group create AH arguments in struct

Following patch adds additional argument to the create AH function, so it
make sense to group ah_attr and flags arguments in struct.

Link: https://lore.kernel.org/r/20200430192146.12863-13-maorg@mellanox.com
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Acked-by: Devesh Sharma <devesh.sharma@broadcom.com>
Acked-by: Gal Pressman <galpress@amazon.com>
Acked-by: Weihang Li <liweihang@huawei.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>