default or selected kernelversion does not have config value CONFIG_SUNRPC_XPRT_RDMA_CLIENT.
Result is shown for kernelversion 6.4.14

RPC over RDMA Client Support

modulename: xprtrdma.ko

configname: CONFIG_SUNRPC_XPRT_RDMA_CLIENT

Linux Kernel Configuration
└─>File systems
└─>Network File Systems
└─>RPC over RDMA Client Support
In linux kernel since version 3.15 (release Date: 2014-06-08)  
This option allows the NFS client to support an RDMA-enabled
transport.

To compile RPC client RDMA transport support as a module,
choose M here: the module will be called xprtrdma.

If unsure, say N.

source code: