bcm63xx: enetsw: switch to netdev_alloc_skb_ip_align

bcm63xx: enetsw: switch to netdev_alloc_skb_ip_align

Increases packet processing performance by 30%.
Tested on BCM6328 320 MHz and iperf3 -M 512 for packet/sec performance.

Before:
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-30.00  sec   120 MBytes  33.7 Mbits/sec  277             sender
[  4]   0.00-30.00  sec   120 MBytes  33.5 Mbits/sec                  receiver

After:
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-30.00  sec   155 MBytes  43.3 Mbits/sec  354             sender
[  4]   0.00-30.00  sec   154 MBytes  43.1 Mbits/sec                  receiver

Signed-off-by: Sieng Piaw Liew <liew.s.piaw@gmail.com>
[Merge patches, amend commit and add patch description]
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>