Each time a listener socket becomes ready, MariaDB calls accept() ten
times (MAX_ACCEPT_RETRY), even if all but the first one return EAGAIN
because there are no more connections.  This causes unnecessary CPU
usage - on our server, the CPU load of that thread, which does nothing
but accept(), saturates one CPU core by ~45%.  The loop should stop
after the first EAGAIN.

Perf report:

    11.01%  mariadbd  libc.so.6          [.] accept4
     6.42%  mariadbd  [kernel.kallsyms]  [k] finish_task_switch.isra.0
     5.50%  mariadbd  [kernel.kallsyms]  [k] _raw_spin_unlock_irqrestore
     5.50%  mariadbd  [kernel.kallsyms]  [k] syscall_enter_from_user_mode
     4.59%  mariadbd  [kernel.kallsyms]  [k] __fget_light
     3.67%  mariadbd  [kernel.kallsyms]  [k] kmem_cache_alloc
     2.75%  mariadbd  [kernel.kallsyms]  [k] fput
     2.75%  mariadbd  [kernel.kallsyms]  [k] mod_objcg_state
     1.83%  mariadbd  [kernel.kallsyms]  [k] __inode_wait_for_writeback
     1.83%  mariadbd  [kernel.kallsyms]  [k] __sys_accept4
     1.83%  mariadbd  [kernel.kallsyms]  [k] _raw_spin_unlock_irq
     1.83%  mariadbd  [kernel.kallsyms]  [k] alloc_inode
     1.83%  mariadbd  [kernel.kallsyms]  [k] call_rcu