MAINTAINERS: rename TC entry and add couple of header files

The section is not specific only to "TC classifiers", but applies to the
whole TC subsystem. Also, add couple of forgotten headers.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>