Parameterise Banner and DebianBanner as defaults

This commit parameterises `Banner` and `DebianBanner` in the sshd config
with the defaults `ssh_banner` and `ssh_print_debian_banner` respectively,
though the latter is only supported on Debian family distributions.

Debian based distributions will have `DebianBanner no` set by default
from now on.

defaults/main.yml

@@ -69,6 +69,12 @@ ssh_print_motd: false      # sshd
 # false to disable display of last login information
 ssh_print_last_log: false    # sshd
 
+# false to disable serving /etc/ssh/banner.txt before authentication is allowed
+ssh_banner: false # sshd
+
+# false to disable distribution version leakage during initial protocol handshake
+ssh_print_debian_banner: false # sshd (Debian OS family only)
+
 # true to enable sftp configuration
 sftp_enabled: false
 

templates/opensshd.conf.j2

@@ -198,10 +198,11 @@ PrintMotd {{ 'yes' if ssh_print_motd else 'no' }}
 
 PrintLastLog {{ 'yes' if ssh_print_last_log else 'no' }}
 
-#Banner /etc/ssh/banner.txt
-#UseDNS yes
-#PidFile /var/run/sshd.pid
-#MaxStartups 10
+Banner {{ '/etc/ssh/banner.txt' if ssh_banner else 'none' }}
+
+{% if ansible_os_family == 'Debian' %}
+DebianBanner {{ 'yes' if ssh_print_debian_banner else 'no' }}
+{% endif %}
 
 {% if sftp_enabled %}
 # Configuration, in case SFTP is used