SUNRPC: Remove svc_rqst::rq_xprt_hlen

[ Upstream commit 983084b2 ]

Clean up: This field is now always set to zero.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: 948f072a ("SUNRPC: always free ctxt when freeing deferred request")
Signed-off-by: Sasha Levin <sashal@kernel.org>