Move change to validate_gas for easier diffs

Putting it back in the original spot from before the branch makes it
easier to see what changed.

Author: carver

eth/validation.py

@@ -228,6 +228,18 @@ def validate_vm_configuration(vm_configuration: Tuple[Tuple[int, Type[VirtualMac
     ))
 
 
+def validate_gas_limit(gas_limit: int, parent_gas_limit: int) -> None:
+    low_bound, high_bound = compute_gas_limit_bounds(parent_gas_limit)
+    if gas_limit < low_bound:
+        raise ValidationError(
+            f"The gas limit {gas_limit} is too low. It must be at least {low_bound}"
+        )
+    elif gas_limit > high_bound:
+        raise ValidationError(
+            f"The gas limit {gas_limit} is too high. It must be at most {high_bound}"
+        )
+
+
 ALLOWED_HEADER_FIELDS = {
     'coinbase',
     'difficulty',
@@ -250,15 +262,3 @@ def validate_header_params_for_configuration(header_params: Dict[str, Any]) -> N
             f"({', '.join(tuple(sorted(ALLOWED_HEADER_FIELDS)))}). "
             f"The provided fields ({', '.join(tuple(sorted(extra_fields)))}) are not supported"
         )
-
-
-def validate_gas_limit(gas_limit: int, parent_gas_limit: int) -> None:
-    low_bound, high_bound = compute_gas_limit_bounds(parent_gas_limit)
-    if gas_limit < low_bound:
-        raise ValidationError(
-            f"The gas limit {gas_limit} is too low. It must be at least {low_bound}"
-        )
-    elif gas_limit > high_bound:
-        raise ValidationError(
-            f"The gas limit {gas_limit} is too high. It must be at most {high_bound}"
-        )