[LTP] Network stress tests fail with Ubuntu

[Elder C. <eld...@te...>]

Under Ubuntu several network stress tests fail due to the use of bash 
specific syntax that Ubuntu's sh (aka dash) does not support.

I have managed to work around them by simply changing the headers of all 
the scripts from #!/bin/sh to #!/bin/bash.

I would like to suggest this change as I think it will have no impact 
over other Linux distros.

I am attaching a script instead of a patch as the latter would be too 
BIG for the task.

Regards.

Elder.

Signed-Off-By: Elder Costa <eld...@te...>