`NetProvider.wait` should not explicitly return errors

[CuriousGeorgiy]

Currently, the EpollNetProvider's wait method returns errors (while the LibevNetProvider does not):

tntcxx/src/Client/EpollNetProvider.hpp

Lines 276 to 281 in a3d0414

	if (event_cnt < 0) {
	//Poll error doesn't belong to any connection so just global
	//log it.
	LOG_ERROR("Poll failed: ", strerror(errno));
	return -1;
	}

tntcxx/src/Client/EpollNetProvider.hpp

Lines 288 to 299 in a3d0414

	if (conn.get_strm().has_status(SS_NEED_READ_EVENT_FOR_WRITE)) {
	int rc = send(conn);
	if (rc < 0)
	return -1;
	}
	/*
	* Once we read all bytes from socket connection
	* becomes ready to decode.
	*/
	int rc = recv(conn);
	if (rc < 0)
	return -1;

tntcxx/src/Client/EpollNetProvider.hpp

Lines 308 to 315 in a3d0414

	if (conn.get_strm().has_status(SS_NEED_WRITE_EVENT_FOR_READ)) {
	int rc = recv(conn);
	if (rc < 0)
	return -1;
	}
	int rc = send(conn);
	if (rc < 0)
	return -1;

However, since the NetProvider manages multiple connections the fact it returns an error when we are waiting for one specific connection is ambiguous. It is not clear how to handle the error on the connector level. Moreover, setting an error for a specific connection based on the wait failure, as we currently do, is obviously wrong:

tntcxx/src/Client/Connector.hpp

Lines 229 to 233 in a3d0414

	if (m_NetProvider.wait(timer.timeLeft()) != 0) {
	conn.setError(std::string("Failed to poll: ") +
	strerror(errno), errno);
	return -1;
	}

tntcxx/src/Client/Connector.hpp

Lines 269 to 273 in a3d0414

	if (m_NetProvider.wait(timer.timeLeft()) != 0) {
	conn.setError(std::string("Failed to poll: ") +
	strerror(errno), errno);
	return -1;
	}

tntcxx/src/Client/Connector.hpp

Lines 328 to 332 in a3d0414

	if (m_NetProvider.wait(timer.timeLeft()) != 0) {
	conn.setError(std::string("Failed to poll: ") +
	strerror(errno), errno);
	return -1;
	}

Instead, we should rely on the NetProvider to mark any connection as faulty, and the NetProvider should be able to overcome any failures internally, like the LibevNetProvider does.