bridge: mrp: Use hlist_head instead of list_head for mrp

bridge: mrp: Use hlist_head instead of list_head for mrp

Replace list_head with hlist_head for MRP list under the bridge.
There is no need for a circular list when a linear list will work.
This will also decrease the size of 'struct net_bridge'.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20201106215049.1448185-1-horatiu.vultur@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>