BUILD: stick-table: fix build error on 32-bit platforms

BUILD: stick-table: fix build error on 32-bit platforms

Commit 9b2717e7b ("MINOR: stktable: use {show,set,clear} table with ptr")
stores a pointer in a long long (64bit), which fails the cas to void* on
32-bit platforms:

  src/stick_table.c: In function 'table_process_entry_per_ptr':
  src/stick_table.c:5136:37: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   5136 |         ts = stktable_lookup_ptr(t, (void *)ptr);

On all our supported platforms, longs and pointers are of the same size,
so let's just turn this to a ulong instead.