bridge: netlink: make br_fill_info's frame size smaller

When KASAN is enabled the frame size grows > 2048 bytes and we get a
warning, so make it smaller.
net/bridge/br_netlink.c: In function 'br_fill_info':
>> net/bridge/br_netlink.c:1110:1: warning: the frame size of 2160 bytes
>> is larger than 2048 bytes [-Wframe-larger-than=]

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>