net: ll_temac: Use GFP_KERNEL instead of GFP_ATOMIC when possible

XTE_MAX_JUMBO_FRAME_SIZE is over 9000 bytes and the default value for
'rx_bd_num' is RX_BD_NUM_DEFAULT	(i.e. 1024)

So this loop allocates more than 9 Mo of memory.

Previous memory allocations in this function already use GFP_KERNEL, so
use __netdev_alloc_skb_ip_align() and an explicit GFP_KERNEL instead of a
implicit GFP_ATOMIC.

This gives more opportunities of successful allocation.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/694abd65418b2b3974106a82d758e3474c65ae8f.1645042560.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>