bsdsocket: implement recfrom(), accept(), name(), peer() using FFI

The reason these function were implemented in Lua/C was complexity of struct sockaddr for ffi.cdef(). However, it is possible to define this structure in FFI in platform-independent way. Please take a look on C preprocessor output and definition in [ljsyscall](https://github.com/justincormack/ljsyscall project).

The plan:

1. Create ffi.cdef() for struct sockaddr
2. Re-implement lbox_bsdsocket_push_family(), lbox_bsdsocket_push_sotype(), lbox_bsdsocket_push_addr() using FFI (without removing existing Lua/C version)
3. Re-implement socket:recfrom() and socket:accept() using FFI
4. Re-implement lbox_bsdsocket_peername() and lbox_bsdsocket_soname() using FFI
5. Split lbox_bsdsocket_getaddrinfo() into two parts:
   • Lua/C version should perform actual name resolution and then push struct addrinfo to Lua stack using luaL_pushcdata() (the code above this line).
   • Lua/FFI version should call Lua/C version, get struct addrinfo, set ffi.gc() on it and create corresponding Lua table with results using new Lua code of lbox_bsdsocket_push_addr().
6. Remove lbox_bsdsocket_push_addr(), lbox_bsdsocket_push_family() and so on.

As result your boxsocket.cc file will contain only two Lua/C functions:

    { "iowait",     lbox_bsdsocket_iowait       },
    { "abort",      lbox_bsdsocket_abort        },
        { NULL,         NULL                }

Please discuss with me how to split this work into patches.

P.S. lbox_socket_abort() will be affected by #880