firewire: core: replace local macros with common inline functions for asynchronous packet header

This commit uses common inline functions to serialize and deserialize
header of asynchronous packet.

Link: https://lore.kernel.org/r/20240428071347.409202-3-o-takashi@sakamocchi.jpSigned-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>