Use int32_t type for most transaction size/weight values

This change gets rid of a few casts and makes the following commit diff
smaller.

test/functional/interface_usdt_mempool.py

@@ -35,7 +35,7 @@ MEMPOOL_TRACEPOINTS_PROGRAM = """
 struct added_event
 {
   u8    hash[HASH_LENGTH];
-  u64   vsize;
+  s32   vsize;
   s64   fee;
 };
 
@@ -43,7 +43,7 @@ struct removed_event
 {
   u8    hash[HASH_LENGTH];
   char  reason[MAX_REMOVAL_REASON_LENGTH];
-  u64   vsize;
+  s32   vsize;
   s64   fee;
   u64   entry_time;
 };
@@ -57,11 +57,11 @@ struct rejected_event
 struct replaced_event
 {
   u8    replaced_hash[HASH_LENGTH];
-  u64   replaced_vsize;
+  s32   replaced_vsize;
   s64   replaced_fee;
   u64   replaced_entry_time;
   u8    replacement_hash[HASH_LENGTH];
-  u64   replacement_vsize;
+  s32   replacement_vsize;
   s64   replacement_fee;
 };