net: bridge: fix vlan stats continue counter

I made a dumb off-by-one mistake when I added the vlan stats counter
dumping code. The increment should happen before the check, not after
otherwise we miss one entry when we continue dumping.

Fixes: a60c0903

 ("bridge: netlink: export per-vlan stats")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>