fru: Update the fru section offset only when they exist (offset is not 0)

[andrew8325]

Fix the issue #364 and also consider other fru section including Board and Product.

[andrew8325]

I upload a new commit, which will do the following things:

• Calculate the section offset one by one according to their offset
• Ignore the FRU section offset if its offset is 00 (area does not exist)
• If the new FRU become smaller, reset the redundant data to 0

After this change, the FRU edit still works normally

Before modify:

root@ubuntu:~$ ipmitool fru print 0               
 Chassis Type          : Rack Mount Chassis
 Chassis Part Number   : ServerNum
 Chassis Serial        : 0123456789
 Chassis Extra         : ---
 Chassis Extra         : ---
 Board Mfg Date        : Mon 26 Sep 2022 06:30:00 PM CST CST
 Board Mfg             : ServerMfc
 Board Product         : ServerName
 Board Part Number     : PartNumber
 Board Extra           : ---
 Board Extra           : ---
 Board Extra           : 00
 Product Manufacturer  : ServerMfc
 Product Name          : ServerName
 Product Part Number   : ServerModel
 Product Version       : Storage
 Product Asset Tag     : ---
 Product Extra         : ---
 Product Extra         : ---
 Product Extra         : ---

Edit Chassis area by command

root@ubuntu:~$ ipmitool fru edit 0 field c 1 ABC    
 String size are not equal, resizing fru to fit new string
 Read All FRU area
 Fru Size       : 512 bytes
 Copy to new FRU
 Section Length: 40
 Padding Length: 6
 NumByte Change: -7
 Start SecChnge: ca
End SecChnge  : 33
 Start Section : 1
 End Sec wo Pad: c1
 End Section   : 47
 New Padding Length: 13
 change_size_by_8: -1
 New Padding Length: 5
 change_size_by_8: -1
 header.offset.board: 6
 Moving Section Board, from 48 to 40
 Moving Section Product, from 112 to 104
 Reset to 0 from 176 to 184
 Updating Field : '0123456789' with 'ABC' ... (Length from '202' to '195')
 Copying remaining of sections: 14 
 Calculate New Checksum: ffffff96
 Writing new FRU.
 Done.

After editing the FRU

root@ubuntu:~$ ipmitool fru print 0
 Chassis Type          : Rack Mount Chassis
 Chassis Part Number   : ServerNum
 Chassis Serial        : ABC
 Chassis Extra         : ---
 Chassis Extra         : ---
 Board Mfg Date        : Mon 26 Sep 2022 06:30:00 PM CST CST
 Board Mfg             : ServerMfc
 Board Product         : ServerName
 Board Part Number     : PartNumber
 Board Extra           : ---
 Board Extra           : ---
 Board Extra           : 00
 Product Manufacturer  : ServerMfc
 Product Name          : ServerName
 Product Part Number   : ServerModel
 Product Version       : Storage
 Product Asset Tag     : ---
 Product Extra         : ---
 Product Extra         : ---
 Product Extra         : ---