[PATCH] netlink: Fix the netlink socket malfunction due to concurrency

[Qingjie Xing]

This piece of code has been present since the Linux code v2.6.12 was
incorporated into Git management.
I believe this modification could potentially address the concurrent issue
we've been discussing.
In netlink_rcv_wake(), as described in [2], the socket's receive queue is
empty, indicated by sk_rmem_alloc being 0. At this point, concurrent
netlink_attachskb() calls netlink_overrun(). In this critical state, the
sk_rmem_alloc of the socket will not instantly transition from 0 to a
value greater than sk_rcvbuf.