Add comments to wireless access point scripts (#1784)

Related #1711

This is a follow-up PR to a [review
comment](https://codeapprove.com/pr/tiny-pilot/tinypilot/1778#thread-4d8c230a-afdd-4361-8e21-0a7be15efb06)
asking for more code comments in our `enable-wifi-ap` and
`disable-wifi-ap` scripts.

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debian-pkg/opt/tinypilot-privileged/scripts/disable-wifi-ap

@@ -51,18 +51,24 @@ readonly SCRIPT_DIR
 # shellcheck source=lib/markers.sh
 . "${SCRIPT_DIR}/lib/markers.sh"
 
+# Clear existing TinyPilot network configurations.
 "${SCRIPT_DIR}/strip-marker-sections" /etc/dhcpcd.conf
 
-mv \
-  /etc/wpa_supplicant/wpa_supplicant.conf.bak \
-  /etc/wpa_supplicant/wpa_supplicant.conf
+# Restore previously backed up WPA configurations.
+if [[ -e /etc/wpa_supplicant/wpa_supplicant.conf.bak ]]; then
+  mv \
+    /etc/wpa_supplicant/wpa_supplicant.conf.bak \
+    /etc/wpa_supplicant/wpa_supplicant.conf
+fi
 
+# Disable WPA.
 if [[ -e /etc/wpa_supplicant/wlan_enabled ]]; then
   rm --force /etc/wpa_supplicant/wlan_enabled
 else
   rfkill block wlan
 fi
 
+# Stop wireless access point.
 systemctl stop hostapd dnsmasq
 rm --force \
   /etc/hostapd/hostapd.conf \

debian-pkg/opt/tinypilot-privileged/scripts/enable-wifi-ap

@@ -124,8 +124,10 @@ readonly SCRIPT_DIR
 # shellcheck source=lib/markers.sh
 . "${SCRIPT_DIR}/lib/markers.sh"
 
+# Clear existing TinyPilot network configurations.
 "${SCRIPT_DIR}/strip-marker-sections" /etc/dhcpcd.conf
 
+# Enable wireless network interface.
 cat <<EOF | tee --append /etc/dhcpcd.conf
 ${MARKER_START}
 interface wlan0
@@ -134,6 +136,7 @@ nohook wpa_supplicant
 ${MARKER_END}
 EOF
 
+# Configure wireless access point.
 cat <<EOF | tee /etc/hostapd/hostapd.conf
 country_code=${NETWORK_COUNTRY}
 interface=wlan0
@@ -150,13 +153,15 @@ wpa_pairwise=TKIP
 rsn_pairwise=CCMP
 EOF
 
+# Configure DHCP server for wireless access point.
 cat <<EOF | tee /etc/dnsmasq.conf
 interface=wlan0
 dhcp-range=${NETWORK_AP_CLIENT_IP_RANGE_START},${NETWORK_AP_CLIENT_IP_RANGE_END},255.255.255.0,24h
 domain=wlan
 address=/gw.wlan/${NETWORK_AP_IP_ADDRESS}
 EOF
 
+# Backup WPA configurations.
 cp \
   --no-clobber \
   /etc/wpa_supplicant/wpa_supplicant.conf \
@@ -166,11 +171,13 @@ if ! rfkill list wlan | grep -q 'yes'; then
   touch /etc/wpa_supplicant/wlan_enabled
 fi
 
+# Clear WPA configurations.
 cat <<'EOF' | tee /etc/wpa_supplicant/wpa_supplicant.conf
 ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
 update_config=1
 EOF
 
+# Start wireless access point.
 rfkill unblock wlan
 systemctl unmask hostapd dnsmasq
 systemctl enable hostapd dnsmasq