Staging: lustre: ptlrpc: service: Declare local functions as static

Declare ptlrpc_server_drop_request and ptlrpc_stop_all_threads
as static since they are used only in this particular file.Also
remove the corresponding declaration from header files.

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>