bridge: Add flag to control mac learning.

Allow user to control whether mac learning is enabled on the port.
By default, mac learning is enabled.  Disabling mac learning will
cause new dynamic FDB entries to not be created for a particular port.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_sysfs_if.c b/net/bridge/br_sysfs_if.c
index a1ef1b6..707f362 100644
--- a/net/bridge/br_sysfs_if.c
+++ b/net/bridge/br_sysfs_if.c
@@ -158,6 +158,7 @@
 BRPORT_ATTR_FLAG(hairpin_mode, BR_HAIRPIN_MODE);
 BRPORT_ATTR_FLAG(bpdu_guard, BR_BPDU_GUARD);
 BRPORT_ATTR_FLAG(root_block, BR_ROOT_BLOCK);
+BRPORT_ATTR_FLAG(learning, BR_LEARNING);
 
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 static ssize_t show_multicast_router(struct net_bridge_port *p, char *buf)
@@ -195,6 +196,7 @@
 	&brport_attr_hairpin_mode,
 	&brport_attr_bpdu_guard,
 	&brport_attr_root_block,
+	&brport_attr_learning,
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 	&brport_attr_multicast_router,
 	&brport_attr_multicast_fast_leave,