SUNRPC: fix race to sk_err after xs_error_report

Since commit 4f8943f808 ("SUNRPC: Replace direct task wakeups from
softirq context") there has been a race to the value of the sk_err if both
XPRT_SOCK_WAKE_ERROR and XPRT_SOCK_WAKE_DISCONNECT are set.  In that case,
we may end up losing the sk_err value that existed when xs_error_report was
called.

Fix this by reverting to the previous behavior: instead of using SO_ERROR
to retrieve the value at a later time (which might also return sk_err_soft),
copy the sk_err value onto struct sock_xprt, and use that value to wake
pending tasks.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Fixes: 4f8943f808 ("SUNRPC: Replace direct task wakeups from softirq context")
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/sunrpc/xprtsock.h

@@ -61,6 +61,7 @@ struct sock_xprt {
 	struct mutex		recv_mutex;
 	struct sockaddr_storage	srcaddr;
 	unsigned short		srcport;
+	int			xprt_err;
 
 	/*
 	 * UDP socket buffer size parameters