net: team: fix incorrect maxattr

The maxattr should be the latest attr value, i.e. array size - 1,
not total array size.

Reported-by:  <syzbot+ecd7e07b4be038658c9f@syzkaller.appspotmail.com>
Fixes: 948dbafc ("net: team: use policy generated by YAML spec")
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20240409092812.3999785-1-liuhangbin@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>