net: dsa: fix off-by-one in maximum bridge ID determination

Prior to the blamed commit, the bridge_num range was from
0 to ds->max_num_bridges - 1. After the commit, it is from
1 to ds->max_num_bridges.

So this check:
if (bridge_num >= max)
return 0;
must be updated to:
if (bridge_num > max)
return 0;

in order to allow the last bridge_num value (==max) to be used.

This is easiest visible when a driver sets ds->max_num_bridges=1.
The observed behaviour is that even the first created bridge triggers
the netlink extack "Range of offloadable bridges exceeded" warning, and
is handled in software rather than being offloaded.

Fixes: 3f9bb0301d50 ("net: dsa: make dp->bridge_num one-based")
Signed-off-by: Vladimir Oltean <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/dsa/dsa.c

···
 		bridge_num = find_next_zero_bit(&dsa_fwd_offloading_bridges,
 						DSA_MAX_NUM_OFFLOADING_BRIDGES,
 						1);
-		if (bridge_num >= max)
+		if (bridge_num > max)
 			return 0;
 
 		set_bit(bridge_num, &dsa_fwd_offloading_bridges);