[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/sunrpc/cache.c b/net/sunrpc/cache.c
index 8e05557..73f053d 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1127,6 +1127,7 @@
 };
 
 static void *c_start(struct seq_file *m, loff_t *pos)
+	__acquires(cd->hash_lock)
 {
 	loff_t n = *pos;
 	unsigned hash, entry;
@@ -1183,6 +1184,7 @@
 }
 
 static void c_stop(struct seq_file *m, void *p)
+	__releases(cd->hash_lock)
 {
 	struct cache_detail *cd = ((struct handle*)m->private)->cd;
 	read_unlock(&cd->hash_lock);