Revert "svcrdma: Add Write chunk WRs to the RPC's Send WR chain"

Revert "svcrdma: Add Write chunk WRs to the RPC's Send WR chain"

Performance regression reported with NFS/RDMA using Omnipath,
bisected to commit e084ee673c77 ("svcrdma: Add Write chunk WRs to
the RPC's Send WR chain").

Tracing on the server reports:

  nfsd-7771  [060]  1758.891809: svcrdma_sq_post_err:
	cq.id=205 cid=226 sc_sq_avail=13643/851 status=-12

sq_post_err reports ENOMEM, and the rdma->sc_sq_avail (13643) is
larger than rdma->sc_sq_depth (851). The number of available Send
Queue entries is always supposed to be smaller than the Send Queue
depth. That seems like a Send Queue accounting bug in svcrdma.

As it's getting to be late in the 6.9-rc cycle, revert this commit.
It can be revisited in a subsequent kernel release.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=218743
Fixes: e084ee673c77 ("svcrdma: Add Write chunk WRs to the RPC's Send WR chain")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>