kernel: update 4.9 to 4.9.51

Refresh patches.
Compile-tested on octeon and x86/64.
Runtime-tested on octeon and x86/64.

Fixes the following CVEs:
- CVE-2017-14106
- CVE-2017-14497

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

target/linux/mediatek/patches-4.9/0048-net-core-add-RPS-balancer.patch

@@ -78,7 +78,7 @@ Signed-off-by: John Crispin <john@phrozen.org>
  		if (cpu_online(tcpu)) {
  			cpu = tcpu;
  			goto done;
-@@ -8426,6 +8478,9 @@ static int __init net_dev_init(void)
+@@ -8427,6 +8479,9 @@ static int __init net_dev_init(void)
  		sd->backlog.weight = weight_p;
  	}