IB/rxe: Do not export module's private function

Function rxe_rcv is used internally in RXE and don't need to be
exported. This patch removes such export declaration.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>