netperf needs to set socket buffer sizes for certain routers

[ssundaresan]

The bismark-netperf script needs to read the active conf file to see if it needs to set the -s and -S options.
http://www.netperf.org/svn/netperf2/trunk/doc/netperf.html#index-g_t_002ds_002c-Test_002dspecific-63

Note that it needs to come after all the main options and after a '--'. We already have one such option - the server data port (which we don't really use), so the update needs to take care of that.