app/testpmd: add flow item spec prefix length
app/testpmd: add flow item spec prefix length

Generating bit-masks from prefix lengths is often more convenient than
providing them entirely (e.g. to define IPv4 and IPv6 subnets).

This commit adds the "prefix" operator that assigns generated bit-masks to
any pattern item specification field.

Signed-off-by: Adrien Mazarguil <9d39ea493ca46c560334f650ac5d4b5ffbcb5cf0@6wind.com>
Acked-by: Olga Shern <94f6c1998eaef6808fd787423400815213eeb35d@mellanox.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk