[NET]: Add some acquires/releases sparse annotations.

Add __acquires() and __releases() annotations to suppress some sparse
warnings.

example of warnings :

net/ipv4/udp.c:1555:14: warning: context imbalance in 'udp_seq_start' - wrong
count at exit
net/ipv4/udp.c:1571:13: warning: context imbalance in 'udp_seq_stop' -
unexpected unlock

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 7153e94..eee7742 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2368,6 +2368,7 @@
  *	in detail.
  */
 void *dev_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(dev_base_lock)
 {
 	struct net *net = seq_file_net(seq);
 	loff_t off;
@@ -2394,6 +2395,7 @@
 }
 
 void dev_seq_stop(struct seq_file *seq, void *v)
+	__releases(dev_base_lock)
 {
 	read_unlock(&dev_base_lock);
 }