Fix the missing unpack function in mmdb-convert.py

src/config/mmdb-convert.py

@@ -77,7 +77,7 @@ def to_int32(s):
 
 def to_int28(s):
     "Parse a pair of big-endian 28-bit integers from bytestring s."
-    a, b = unpack("!LL", s + b'\x00')
+    a, b = struct.unpack("!LL", s + b'\x00')
     return (((a & 0xf0) << 20) + (a >> 8)), ((a & 0x0f) << 24) + (b >> 8)
 
 class Tree(object):