nonblock flag is lost during reconnect

[OKriw]

When logging to syslog we suffer from loss O_NONBLOCK flag and tarantool locks on write, that won't happen, because internal socket buffer is full.
How to reproduce:

#!/usr/bin/env tarantool                                                        
                                                                               
socket = require('socket')                                                      
log = require('log')                                                            
fio = require('fio')                                                            
                                                                                
path = fio.pathjoin(fio.cwd(), 'log_unix_socket_test.sock')                     
unix_socket = socket('AF_UNIX', 'SOCK_DGRAM', 0)                                
unix_socket:bind('unix/', path)                                                 
                                                                                
opt = string.format("syslog:server=unix:%s,identity=tarantool", path)           
res = 1                                                                         
buf = 'Started\n'                                                               
box.cfg{log = opt}                                               
log.info("Test socket syslog destination")                                                                                                   
while unix_socket:readable(1) do                                                                                                                 
    buf = buf .. unix_socket:recv(1000)                                         
    if buf:match('Test socket syslog destination') then res = 0 end             
end                                                                             
                                                                                
unix_socket:close()                                                             
os.remove(path)                                                                 
os.exit(res)       

Set log_nonblock is helpless - because we lose O_NONBLOCK when we do recconect to socket. So, tarantool hangs forever.