Staging: lustre: lnet: selftest: Made a function static.

The following patch makes a function static as it was not used by other
files.
The patch fixes the warning:
WARNING: symbol 'brw_fill_bulk' was not declared. Should it be
static?

The above warning was reported by sparse.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>