xprtrdma: Clean up rpcrdma_create_rep() and rpcrdma_destroy_rep()

For code legibility, clean up the function names to be consistent
with the pattern: "rpcrdma" _ object-type _ action

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>