net: ethernet: mtk_eth_soc: Use ipv6_addr_{cpu_to_be32,be32_to_cpu} helpers

net: ethernet: mtk_eth_soc: Use ipv6_addr_{cpu_to_be32,be32_to_cpu} helpers

Use ipv6_addr_cpu_to_be32 and ipv6_addr_be32_to_cpu helpers to convert
address, rather than open coding the conversion.

No functional change intended.
Compile tested only.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/netdev/c7684349-535c-45a4-9a74-d47479a50020@lunn.ch/
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240813-ipv6_addr-helpers-v2-2-5c974f8cca3e@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>