do not persist sysctl when value is invalid

the order of actions for setting, persisting and activation is changed,
to not persist an invalid sysctl value. This is only enforced when
sysct_set is True.

plugins/modules/sysctl.py

@@ -182,12 +182,12 @@ class SysctlModule(object):
 
         # Do the work
         if not self.module.check_mode:
+            if self.set_proc:
+                self.set_token_value(self.args['name'], self.args['value'])
             if self.write_file:
                 self.write_sysctl()
             if self.changed and self.args['reload']:
                 self.reload_sysctl()
-            if self.set_proc:
-                self.set_token_value(self.args['name'], self.args['value'])
 
     def _values_is_equal(self, a, b):
         """Expects two string values. It will split the string by whitespace

tests/integration/targets/sysctl/tasks/main.yml

@@ -289,3 +289,24 @@
           - sysctl_check_mode2 is changed
           - "'vm.swappiness=22' in sysctl_check_mode_conf_content.stdout_lines"
           - sysctl_check_mode_current_vm_swappiness.stdout == '22'
+
+    # Test sysctl: invalid value
+    - name: Set invalid sysctl property using module
+      sysctl:
+        name: vm.mmap_rnd_bits
+        value: '1024'
+        state: present
+        reload: yes
+        sysctl_set: True
+      ignore_errors: True
+      register: sysctl_invalid_set1
+
+    - name: Read /etc/sysctl.conf
+      command: 'cat /etc/sysctl.conf'
+      register: sysctl_invalid_conf_content
+
+    - name: Ensure changes were not made
+      assert:
+        that:
+          - sysctl_invalid_set1 is failed
+          - "'vm.mmap_rnd_bits' not in sysctl_invalid_conf_content.stdout"