net: avoid to call skb_queue_len again

the queue length of sd->input_pkt_queue has been put into qlen,
and impossible to change, since hold the lock

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>