Add a definition and a comment

include/netinet/in.h

@@ -80,6 +80,7 @@
 #define IPPROTO_COMP          108  /* Compression Header protocol */
 #define IPPROTO_SCTP          132  /* Stream Control Transport Protocol */
 #define IPPROTO_UDPLITE       136  /* UDP-Lite (RFC 3828) */
+#define IPPROTO_MPLS          137  /* MPLS in IP (RFC 4023) */
 #define IPPROTO_RAW           255  /* Raw IP packets */
 
 /* Values used with SIOCSIFMCFILTER and SIOCGIFMCFILTER ioctl's */

include/nuttx/sched.h

@@ -430,6 +430,8 @@ struct task_group_s
 #endif
 
 #ifndef HAVE_GROUP_MEMBERS
+  /* REVISIT: What if parent thread exits?  Should use tg_pgid. */
+
   pid_t    tg_ppid;                 /* This is the ID of the parent thread      */
 #ifndef CONFIG_SCHED_CHILD_STATUS
   uint16_t tg_nchildren;            /* This is the number active children       */