raise systemd LimitNOFILE limits to match server defaults (~32768)

Starting MariaDB with default configuration causes the following problems:

• "[Warning] Could not increase number of max_open_files to more than 16384 (request: 32186)"
• silently reduces table_open_cache_instances from 8 (default) to 4

Default Server System Variables:

• extra_max_connections = 1
• max_connections = 151
• table_open_cache = 2000
• table_open_cache_instances = 8
• thread_pool_size = 4

LimitNOFILE=16834 is in the following files:

• support-files/mariadb.service.in
• support-files/mariadb@.service.in

Looking at sql/mysqld.cc lines 3837-3917:
wanted_files= (extra_files + max_connections + extra_max_connections +
tc_size * 2 * tc_instances);
wanted_files+= threadpool_size;

Plugging in the default values:
wanted_files = (30 + 151 + 1 + 2000 * 2 * 8 + 4) = 32186

However, systemd configuration has LimitNOFILE = 16384, which is far smaller.

I suggest increasing LimitNOFILE to 32768.

Thank you!
Daniel Lewart
Urbana, Illinois