qed: fix LL2 RX buffer allocation

Driver allocates the LL2 rx buffers from kmalloc()
area to construct the skb using slab_build_skb()

The required size allocation seems to have overlooked
for accounting both skb_shared_info size and device
placement padding bytes which results into the below
panic when doing skb_put() for a standard MTU sized frame.

skbuff: skb_over_panic: text:ffffffffc0b0225f len:1514 put:1514
head:ff3dabceaf39c000 data:ff3dabceaf39c042 tail:0x62c end:0x566
dev:<NULL>
…
skb_panic+0x48/0x4a
skb_put.cold+0x10/0x10
qed_ll2b_complete_rx_packet+0x14f/0x260 [qed]
qed_ll2_rxq_handle_completion.constprop.0+0x169/0x200 [qed]
qed_ll2_rxq_completion+0xba/0x320 [qed]
qed_int_sp_dpc+0x1a7/0x1e0 [qed]

This patch fixes this by accouting skb_shared_info and device
placement padding size bytes when allocating the buffers.

Cc: David S. Miller <davem@davemloft.net>
Fixes: 0a7fb11c

 ("qed: Add Light L2 support")
Signed-off-by: Manish Chopra <manishc@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>