RDMA/rxe: Fix __bth_set_resv6a

__bth_set_resv6a is used to clear BIT [24, 29] of rxe_bth::qpn, the
wrong expression leads other BITs into 1.

Link: https://patch.msgid.link/r/20240822065223.1117056-4-pizhenwei@bytedance.com


Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>