net: sockets: Check eventfd errors better

With native_sim, this error is seen a lot when socket
service API is used.

  <dbg> net_sock: get_sock_vtable: (net_socket_service):
    Invalid access on sock 3 by thread 0x807a8e0 (net_socket_service)

If we just ignore the error, then we might get into forever
loop which is not good. So if this happens, mark the eventfd
fd as not pollable to basically ignore the eventfd support in
this case.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>