kernel: bump 4.9 to 4.9.77

kernel: bump 4.9 to 4.9.77

Refresh patches.
Remove upstreamed patches:

target/linux/generic/backport-4.9/023-2-smsc75xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch
target/linux/generic/backport-4.9/023-3-cx82310_eth-use-skb_cow_head-to-deal-with-cloned-skb.patch
target/linux/generic/backport-4.9/023-4-sr9700-use-skb_cow_head-to-deal-with-cloned-skbs.patch
target/linux/generic/backport-4.9/023-5-lan78xx-use-skb_cow_head-to-deal-with-cloned-skbs.patch

CVEs completely or partially addressed:

CVE-2017-5715
CVE-2017-5753
CVE-2017-17741
CVE-2017-1000410

Compile-tested: ar71xx Archer C7 v2
Run-tested: ar71xx Archer C7 v2

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
Tested-by: Koen Vandeputte <koen.vandeputte@ncentric.com>