tipc: use min() to simplify the code

When calculating size of own domain based on number of peers, the result
should be less than MAX_MON_DOMAIN, so using min() here is very semantic.

Signed-off-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240822133908.1042240-8-lizetao1@huawei.com


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