net: tipc: replace align() with ALIGN in msg.c

The function align() which is defined in msg.c is redundant, replace it
with ALIGN() and introduce a BUF_ALIGN().

Signed-off-by: Menglong Dong <dong.menglong@zte.com.cn>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>