RDMA/rxe: Check the last packet by RXE_END_MASK

It's wrong to check the last packet by RXE_COMP_MASK because the flag is
to indicate if responder needs to generate a completion.

Fixes: 9fcd67d1 ("IB/rxe: increment msn only when completing a request")
Fixes: 8700e3e7 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20211229034438.1854908-1-yangx.jy@fujitsu.com


Signed-off-by: Xiao Yang <yangx.jy@fujitsu.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>