tcp: add tracepoint trace_tcp_set_state()

This patch adds tracepoint trace_tcp_set_state. Besides usual fields
(s/d ports, IP addresses), old and new state of the socket is also
printed with TP_printk, with __print_symbolic().

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>