docs: networking: convert tc-actions-env-rules.txt to ReST

- add SPDX header;
- add a document title;
- use the right numbered list markup;
- adjust identation, whitespaces and blank lines where needed;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/index.rst

···
    skfp
    strparser
    switchdev
+   tc-actions-env-rules
 
 .. only::  subproject and html
 

Documentation/networking/tc-actions-env-rules.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+================================
+TC Actions - Environmental Rules
+================================
+
+
+The "environmental" rules for authors of any new tc actions are:
+
+1) If you stealeth or borroweth any packet thou shalt be branching
+   from the righteous path and thou shalt cloneth.
+
+   For example if your action queues a packet to be processed later,
+   or intentionally branches by redirecting a packet, then you need to
+   clone the packet.
+
+2) If you munge any packet thou shalt call pskb_expand_head in the case
+   someone else is referencing the skb. After that you "own" the skb.
+
+3) Dropping packets you don't own is a no-no. You simply return
+   TC_ACT_SHOT to the caller and they will drop it.
+
+The "environmental" rules for callers of actions (qdiscs etc) are:
+
+#) Thou art responsible for freeing anything returned as being
+   TC_ACT_SHOT/STOLEN/QUEUED. If none of TC_ACT_SHOT/STOLEN/QUEUED is
+   returned, then all is great and you don't need to do anything.
+
+Post on netdev if something is unclear.

Documentation/networking/tc-actions-env-rules.txt

···
-
-The "environmental" rules for authors of any new tc actions are:
-
-1) If you stealeth or borroweth any packet thou shalt be branching
-from the righteous path and thou shalt cloneth.
-
-For example if your action queues a packet to be processed later,
-or intentionally branches by redirecting a packet, then you need to
-clone the packet.
-
-2) If you munge any packet thou shalt call pskb_expand_head in the case
-someone else is referencing the skb. After that you "own" the skb.
-
-3) Dropping packets you don't own is a no-no. You simply return
-TC_ACT_SHOT to the caller and they will drop it.
-
-The "environmental" rules for callers of actions (qdiscs etc) are:
-
-*) Thou art responsible for freeing anything returned as being
-TC_ACT_SHOT/STOLEN/QUEUED. If none of TC_ACT_SHOT/STOLEN/QUEUED is
-returned, then all is great and you don't need to do anything.
-
-Post on netdev if something is unclear.
-