docs: bridge: update doc format to rst

The current bridge kernel doc is too old. It only pointed to the
linuxfoundation wiki page which lacks of the new features.

Here let's start the new bridge document and put all the bridge info
so new developers and users could catch up the last bridge status soon.

In this patch, Convert the doc to rst format. Add bridge brief introduction,
FAQ and contact info.
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/networking/bridge.rst

@@ -4,18 +4,45 @@
 Ethernet Bridging
 =================
 
-In order to use the Ethernet bridging functionality, you'll need the
-userspace tools.
+Introduction
+============
 
-Documentation for Linux bridging is on:
-   https://wiki.linuxfoundation.org/networking/bridge
+The IEEE 802.1Q-2022 (Bridges and Bridged Networks) standard defines the
+operation of bridges in computer networks. A bridge, in the context of this
+standard, is a device that connects two or more network segments and operates
+at the data link layer (Layer 2) of the OSI (Open Systems Interconnection)
+model. The purpose of a bridge is to filter and forward frames between
+different segments based on the destination MAC (Media Access Control) address.
 
-The bridge-utilities are maintained at:
-   git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/bridge-utils.git
+FAQ
+===
 
-Additionally, the iproute2 utilities can be used to configure
-bridge devices.
+What does a bridge do?
+----------------------
 
-If you still have questions, don't hesitate to post to the mailing list 
-(more info https://lists.linux-foundation.org/mailman/listinfo/bridge).
+A bridge transparently forwards traffic between multiple network interfaces.
+In plain English this means that a bridge connects two or more physical
+Ethernet networks, to form one larger (logical) Ethernet network.
 
+Is it L3 protocol independent?
+------------------------------
+
+Yes. The bridge sees all frames, but it *uses* only L2 headers/information.
+As such, the bridging functionality is protocol independent, and there should
+be no trouble forwarding IPX, NetBEUI, IP, IPv6, etc.
+
+Contact Info
+============
+
+The code is currently maintained by Roopa Prabhu <roopa@nvidia.com> and
+Nikolay Aleksandrov <razor@blackwall.org>. Bridge bugs and enhancements
+are discussed on the linux-netdev mailing list netdev@vger.kernel.org and
+bridge@lists.linux-foundation.org.
+
+The list is open to anyone interested: http://vger.kernel.org/vger-lists.html#netdev
+
+External Links
+==============
+
+The old Documentation for Linux bridging is on:
+https://wiki.linuxfoundation.org/networking/bridge