pktgen: new pktgen helper functions for samples scripts

Preparing for removing existing samples/pktgen/ scripts, and
replacing these with easier to use samples.

This commit provides two helper shell files, that can
be "included" by shell source'ing. Namely "functions.sh"
and "parameters.sh".

The parameters.sh file support easy and consistant parameter
parsing across the sample scripts.  Usage example is printed on
errors.

The functions.sh file provides, three new shell functions for
configuring the different components of pktgen: pg_ctrl(),
pg_thread() and pg_set().  A slightly improved version of the old
pgset() function is also provided for backwards compat.

The new functions correspond to pktgens different components.
 * pg_ctrl()   control "pgctrl" (/proc/net/pktgen/pgctrl)
 * pg_thread() control the kernel threads and binding to devices
 * pg_set()    control setup of individual devices

These changes are borrowed from:
 https://github.com/netoptimizer/network-testing/tree/master/pktgen



Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>