Netlink conn retry logic

[turekt]

Hi,

I have introduced an additional function to the conn.go file which implements receive of netlink messages with retries. This should fix issue #175.

For some reason, in a lasting connection netlink sends a "no error" message with NLM_F_CAPPED flag set, and afterwards sends the actual message. Therefore, since there is nothing special to handle upon receiving the NLM_F_CAPPED + "no error" message, we can just drop the message and receive the next non-error message which should be the expected response.

Let me know what you think about this approach.