netatop: fix compilation warning for kernel module

Fix compilation warning for missing fallthrough.
Fix compilation warning:
/builder/shared-workdir/build/build_dir/target-mipsel_24kc_musl/netatop-3.1/module/netatop.c: In function 'getsockopt':
/builder/shared-workdir/build/build_dir/target-mipsel_24kc_musl/netatop-3.1/module/netatop.c:1619:26: error: this statement may fall through [-Werror=implicit-fallthrough=]
 1619 |                 tasktype = 'g';
      |                 ~~~~~~~~~^~~~~
/builder/shared-workdir/build/build_dir/target-mipsel_24kc_musl/netatop-3.1/module/netatop.c:1621:12: note: here
 1621 |            case NETATOP_GETCNT_PID:
      |            ^~~~
cc1: all warnings being treated as errors
Signed-off-by: NChristian Marangi <ansuelsmth@gmail.com>

admin/netatop/patches/100-fix-compilation-warning-fallthrough.patch

+--- a/module/netatop.c
++++ b/module/netatop.c
+@@ -1617,7 +1617,7 @@ getsockopt(struct sock *sk, int cmd, void __user *user, int *len)
+ 
+  	   case NETATOP_GETCNT_TGID:
+ 		tasktype = 'g';		
+-		// fall through
++		fallthrough;
+  	   case NETATOP_GETCNT_PID:
+ 		if (*len < sizeof(pid_t))
+ 			return -EINVAL;