test/et/et: use evutil_socket_t* over int* for pointer to the pair

test/et/et: use evutil_socket_t* over int* for pointer to the pair

Next code will not work correctly under win x64:
  evutil_socket_t very_long_pair_name[2];
  int *pair = very_long_pair_name; // <-- accessing the second word of the first element

Because sizeof(evutil_socket_t) == sizeof(intptr_t) == 8

P.S. in the 5334762f another test had been fixed instead of the one that
really fails.

Fixes: 5334762f ("test/et/et: fix it by using appropriate type for the SOCKET (evutil_socket_t)")
Refs: #750