selinux: reduce the number of calls to synchronize_net() when flushing caches

When flushing the AVC, such as during a policy load, the various
network caches are also flushed, with each making a call to
synchronize_net() which has shown to be expensive in some cases.
This patch consolidates the network cache flushes into a single AVC
callback which only calls synchronize_net() once for each AVC cache
flush.

Reported-by: Jaejyn Shin <flagon22bass@gmail.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>

security/selinux/include/netnode.h

@@ -27,6 +27,8 @@
 #ifndef _SELINUX_NETNODE_H
 #define _SELINUX_NETNODE_H
 
+void sel_netnode_flush(void);
+
 int sel_netnode_sid(void *addr, u16 family, u32 *sid);
 
 #endif