[PACKET]: Fix sparse warnings in af_packet.c

[Eric Dumazet <dada1@cosmosbay.com>]

  CHECK   net/packet/af_packet.c
net/packet/af_packet.c:1876:14: warning: context imbalance in 'packet_seq_start' - wrong count at exit
net/packet/af_packet.c:1888:13: warning: context imbalance in 'packet_seq_stop' - unexpected unlock

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 43e49f4..b8b827c 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1870,6 +1870,7 @@ static inline struct sock *packet_seq_idx(struct net *net, loff_t off)
 }
 
 static void *packet_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(seq_file_net(seq)->packet.sklist_lock)
 {
 	struct net *net = seq_file_net(seq);
 	read_lock(&net->packet.sklist_lock);
@@ -1886,6 +1887,7 @@ static void *packet_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void packet_seq_stop(struct seq_file *seq, void *v)
+	__releases(seq_file_net(seq)->packet.sklist_lock)
 {
 	struct net *net = seq_file_net(seq);
 	read_unlock(&net->packet.sklist_lock);