xprtrdma: Modernize htonl and ntohl

Clean up: Replace htonl and ntohl with the be32 equivalents.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>