net_sched: act_gact: read tcfg_ptype once

Third step for gact RCU operation :

Following patch will get rid of spinlock protection,
so we need to read tcfg_ptype once.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>