Documentation: sysctl: align cells in second content column

Stephen Rothwell reported htmldocs warning when merging net-next tree:

Documentation/admin-guide/sysctl/net.rst:37: WARNING: Malformed table.
Text in column margin in table line 4.

========= =================== = ========== ==================
Directory Content               Directory  Content
========= =================== = ========== ==================
802       E802 protocol         mptcp     Multipath TCP
appletalk Appletalk protocol    netfilter Network Filter
ax25      AX25                  netrom     NET/ROM
bridge    Bridging              rose      X.25 PLP layer
core      General parameter     tipc      TIPC
ethernet  Ethernet protocol     unix      Unix domain sockets
ipv4      IP version 4          x25       X.25 protocol
ipv6      IP version 6
========= =================== = ========== ==================

The warning above is caused by cells in second "Content" column of
/proc/sys/net subdirectory table which are in column margin.

Align these cells against the column header to fix the warning.

Link: https://lore.kernel.org/linux-next/20220823134905.57ed08d5@canb.auug.org.au/
Fixes: 1202cdd665 ("Remove DECnet support from kernel")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20220824035804.204322-1-bagasdotme@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/admin-guide/sysctl/net.rst

@@ -31,18 +31,18 @@ see only some of them, depending on your kernel's configuration.
 
 Table : Subdirectories in /proc/sys/net
 
- ========= =================== = ========== ==================
+ ========= =================== = ========== ===================
  Directory Content               Directory  Content
- ========= =================== = ========== ==================
- 802       E802 protocol         mptcp     Multipath TCP
- appletalk Appletalk protocol    netfilter Network Filter
+ ========= =================== = ========== ===================
+ 802       E802 protocol         mptcp      Multipath TCP
+ appletalk Appletalk protocol    netfilter  Network Filter
  ax25      AX25                  netrom     NET/ROM
- bridge    Bridging              rose      X.25 PLP layer
- core      General parameter     tipc      TIPC
- ethernet  Ethernet protocol     unix      Unix domain sockets
- ipv4      IP version 4          x25       X.25 protocol
+ bridge    Bridging              rose       X.25 PLP layer
+ core      General parameter     tipc       TIPC
+ ethernet  Ethernet protocol     unix       Unix domain sockets
+ ipv4      IP version 4          x25        X.25 protocol
  ipv6      IP version 6
- ========= =================== = ========== ==================
+ ========= =================== = ========== ===================
 
 1. /proc/sys/net/core - Network core options
 ============================================