Fix a pointer truncation in socket liveness check

Socket liveness check ocasionally failed due to the buffer pointer
truncation that was passed to libc's recv via ctypes, triggering
reconnection, causing general slowdown.

Author: mejedi

tarantool/connection.py

@@ -63,11 +63,6 @@ class Connection(object):
     Also this class provides low-level interface to data manipulation
     (insert/delete/update/select).
     '''
-    _libc = ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
-    _sys_recv = ctypes.CFUNCTYPE(c_ssize_t, ctypes.c_int, ctypes.c_void_p,
-                                 c_ssize_t, ctypes.c_int,
-                                 use_errno=True)(_libc.recv)
-
     Error = tarantool.error
     DatabaseError = tarantool.error.DatabaseError
     InterfaceError = tarantool.error.InterfaceError
@@ -90,6 +85,11 @@ def __init__(self, host, port,
         creates network connection.
                              if False than you have to call connect() manualy.
         '''
+        libc = ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
+        recv = self._sys_recv = libc.recv
+        recv.argtypes = [
+            ctypes.c_int, ctypes.c_void_p, c_ssize_t, ctypes.c_int]
+        recv.restype = c_ssize_t
         self.host = host
         self.port = port
         self.user = user