kernel: support the case that init_task.mnt_ns != zygote.mnt_ns(WSA) (#698)

Basic support for the case that init_task.mnt_ns != zygote.mnt_ns(WSA),
just copy nsproxy and fs pointers for solve #276.

Note the copy in `apk_sign.c` is not required but suggested for
secure(ensure the checked mnt_ns is what ns android running, not created
by user, although many distributions does not have user ns.).

Tested with latest release on Win10 19045.3086(with WSAPatch).

Further review required for:
- [x] Security of this operation (without locking).
- [x] The impact of these modifications on other Android distributions.

kernel/ksud.c

@@ -178,6 +178,7 @@ int ksu_handle_execveat_ksud(int *fd, struct filename **filename_ptr,
 					pr_info("/system/bin/init second_stage executed\n");
 					apply_kernelsu_rules();
 					init_second_stage_executed = true;
+					ksu_android_ns_fs_check();
 				}
 			} else {
 				pr_err("/system/bin/init parse args err!\n");
@@ -194,6 +195,7 @@ int ksu_handle_execveat_ksud(int *fd, struct filename **filename_ptr,
 			// 2: /system/bin/init second_stage
 			pr_info("/system/bin/init second_stage executed\n");
 			apply_kernelsu_rules();
+			ksu_android_ns_fs_check();
 		}
 #endif
 	}