flower: Represent HW traffic classes as classid values

This patch was previously submitted as RFC. Submitting this as
non-RFC now that the classid reservation scheme for hardware
traffic classes and offloads to route packets to a hardware
traffic class are accepted in net-next.

HW traffic classes 0 through 15 are represented using the
reserved classid values :ffe0 - :ffef.

Example:
Match Dst IPv4,Dst Port and route to TC1:
# tc filter add dev eth0 protocol ip parent ffff:\
  prio 1 flower dst_ip 192.168.1.1/32\
  ip_proto udp dst_port 12000 skip_sw\
  hw_tc 1

# tc filter show dev eth0 parent ffff:
filter pref 1 flower chain 0
filter pref 1 flower chain 0 handle 0x1 hw_tc 1
  eth_type ipv4
  ip_proto udp
  dst_ip 192.168.1.1
  dst_port 12000
  skip_sw
  in_hw

Signed-off-by: Amritha Nambiar <amritha.nambiar@intel.com>