[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/netlink/af_netlink.c b/net/netlink/af_netlink.c
index dbd7cad..be07f1b 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -171,6 +171,7 @@
  */
 
 static void netlink_table_grab(void)
+	__acquires(nl_table_lock)
 {
 	write_lock_irq(&nl_table_lock);
 
@@ -193,6 +194,7 @@
 }
 
 static inline void netlink_table_ungrab(void)
+	__releases(nl_table_lock)
 {
 	write_unlock_irq(&nl_table_lock);
 	wake_up(&nl_table_wait);
@@ -1728,6 +1730,7 @@
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(nl_table_lock)
 {
 	read_lock(&nl_table_lock);
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
@@ -1776,6 +1779,7 @@
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
+	__releases(nl_table_lock)
 {
 	read_unlock(&nl_table_lock);
 }