examples/ip_pipeline: enable promiscuous mode configuration

examples/ip_pipeline: enable promiscuous mode configuration

This patch allows parser to read promisc entry from
the LINK section defined in configuration file. It
is an optional parameter: if present, value should
be read (yes/no, on/off), else the value is the
default value (i.e. 1 = promiscuous mode on)

Example of config file:
[LINK0]
promisc = no; optional parameter, default value is “yes”

Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>