The MANA driver's RX buffer alloc_size is passed into napi_build_skb() to
create SKB. skb_shinfo(skb) is located at the end of skb, and its alignment
is affected by the alloc_size passed into napi_build_skb(). The size needs
to be aligned properly for better performance and atomic operations.
Otherwise, on ARM64 CPU, for certain MTU settings like 4000, atomic
operations may panic on the skb_shinfo(skb)->dataref due to alignment fault.

To fix this bug, add proper alignment to the alloc_size calculation.

Sample panic info:
[  253.298819] Unable to handle kernel paging request at virtual address ffff000129ba5cce
[  253.300900] Mem abort info:
[  253.301760]   ESR = 0x0000000096000021
[  253.302825]   EC = 0x25: DABT (current EL), IL = 32 bits
[  253.304268]   SET = 0, FnV = 0
[  253.305172]   EA = 0, S1PTW = 0
[  253.306103]   FSC = 0x21: alignment fault
Call trace:
 __skb_clone+0xfc/0x198
 skb_clone+0x78/0xe0
 raw6_local_deliver+0xfc/0x228
 ip6_protocol_deliver_rcu+0x80/0x500
 ip6_input_finish+0x48/0x80
 ip6_input+0x48/0xc0
 ip6_sublist_rcv_finish+0x50/0x78
 ip6_sublist_rcv+0x1cc/0x2b8
 ipv6_list_rcv+0x100/0x150
 __netif_receive_skb_list_core+0x180/0x220
 netif_receive_skb_list_internal+0x198/0x2a8
 __napi_poll+0x138/0x250
 net_rx_action+0x148/0x330
 handle_softirqs+0x12c/0x3a0

Cc: stable@vger.kernel.org
Fixes: 80f6215b ("net: mana: Add support for jumbo frame")
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>