net: stmmac: selftests: Make it work in Synopsys AXS101 boards

Synopsys AXS101 boards do not support unaligned memory loads or stores.
Change the selftests mechanism to explicity:
- Not add extra alignment in TX SKB
- Use the unaligned version of ether_addr_equal()

Fixes: 091810db ("net: stmmac: Introduce selftests support")
Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>