Several proposed changes to v1model standard_metadata for cheat sheet (#255)

* Several proposed changes to v1model standard_metadata for cheat sheet

Remove several fields that are deprecated in the v1model.p4 include file,
or will be soon:

+ drop
+ recirculate_port
+ clone_spec
+ lf_field_list
+ resubmit_flag
+ recirculate_flag

Add mention of more detailed documentation in behavioral-model
repository, for those that want to know more about how each field
behaves.

Group the fields by those that are only intended to be read in a P4
program, versues read/write, and which are only intended to be useful
in ingress, egress, or both.

* Minor updates to proposed v1model standard_metadata changes

utils/cheat_sheet_src/src/v1model_std_metadata.txt

@@ -1,22 +1,26 @@
 struct standard_metadata_t {
+    // For more details see docs/simple_switch.md
+    // in https://github.com/p4lang/behavioral-model
+
+    // Should only read, ingress or egress
     bit<9>  ingress_port;
-    bit<9>  egress_spec;
-    bit<9>  egress_port;
-    bit<32> clone_spec;
     bit<32> instance_type;
-    bit<1>  drop;
-    bit<16> recirculate_port;
     bit<32> packet_length;
+    bit<48> ingress_global_timestamp;
+    bit<1>  checksum_error;
+    error   parser_error;
+
+    // In ingress, read or write.
+    // In egress, should only read.
+    bit<9>  egress_spec;
+    bit<16> mcast_grp;
+
+    // Should only read, only in egress
+    bit<9>  egress_port;
+    bit<16> egress_rid;
+    bit<48> egress_global_timestamp;
     bit<32> enq_timestamp;
     bit<19> enq_qdepth;
     bit<32> deq_timedelta;
     bit<19> deq_qdepth;
-    bit<48> ingress_global_timestamp;
-    bit<48> egress_global_timestamp;
-    bit<32> lf_field_list;
-    bit<16> mcast_grp;
-    bit<32> resubmit_flag;
-    bit<16> egress_rid;
-    bit<1>  checksum_error;
-    bit<32> recirculate_flag;
-}
+}