390e07d591
Since f3bcd4d205 ("Merge 'Support SSL Certificate Hot
Reloading' from Calle"), we reload certificates as they are
modified on disk. This uses inotify, which is limited by a
sysctl fs.inotify.max_user_instances, with a default of 128.
This is enough for 64 shards only, if both rpc and cql are
encrypted; above that startup fails.
Increase to 1200, which is enough for 6 instances * 200 shards.
Fixes #7700.
Closes #7701