Allocate buffer for 256 entries for ACL resource query

[prsunny]

What I did
Allocate an initial buffer instead of NULL during ACL table/group query

Why I did it
During every CRM polling interval, the following WARNING message is observed. This fix will suppress the frequent WARNINGs

Jun 11 20:23:07.092436 str-a7060cx-acs-1 WARNING syncd: :- processEvent: get API for key: SAI_OBJECT_TYPE_SWITCH:oid:0x21000000000000 op: get returned status: SAI_STATUS_BUFFER_OVERFLOW

How I verified it
Load the changes and verify for WARNING message.
RUN CRM test and also the following commands:

admin@str-a7060cx-acs-1:~$ crm show resources acl table
Table ID         Resource Name      Used Count    Available Count
---------------  ---------------  ------------  -----------------
0x700000000093c  acl_entry                   2               1278

admin@str-a7060cx-acs-1:~$ crm show resources acl group
Stage    Bind Point    Resource Name      Used Count    Available Count
-------  ------------  ---------------  ------------  -----------------
INGRESS  PORT          acl_group                  56                968
INGRESS  PORT          acl_table                   1                  2
INGRESS  LAG           acl_group                   0                968
INGRESS  LAG           acl_table                   0                  4
...

Details if related

[zhenggen-xu]

Can we define this number as a macro?