snort3: unified configs: local.lua and homenet.lua

snort3: unified configs: local.lua and homenet.lua

This commit adds /etc/snort/local.lua and /etc/snort/homenet.lua for user
defined config options which is more simplistic than modifying upstream
files directly. That can be tedious and decisive to maintain in sync with
upstream changes.  The init script has been adjusted accordingly.

Acknowledgment to amish who maintains the Arch Linux snort-nfqueue package[1]
for these ideas and initial code.

Another modification is dropping the following args in the call to
/usr/bin/snort by the init system as these options are provided in
/etc/snort/local.lua:

 * --daq-dir /usr/lib/daq/
 * -A "$alert_module"

Instructions to configure snort3:
1. Edit /etc/snort/homenet.lua and redefine HOME_NET and EXTERNAL_NET, for example:

   HOME_NET = [[ 10.9.8.0/24 192.168.1.0/24 ]]
   EXTERNAL_NET = "!$HOME_NET"

2. Edit /etc/snort/local.lua to setup options unique to your use case of snort.
   The default ones I included should be sane for the role of IDS (alert only),
   but users may easily uncomment some options therein to use IPS (drop) mode.

3. Install or symlink rules to /etc/snort/rules/snort.rules and optionally
   edit /etc/snort/local.lua to define extra rules files if not using a unified
   'snort.rules'

References:
1. https://aur.archlinux.org/packages/snort-nfqueue

Signed-off-by: John Audia <therealgraysky@proton.me>