hostapd: adapt recipe for read-only-rootfs

The access point configuration files are dynamically modified on a post
install script to generate an SSID name based on the last digits of the
MAC address (physical or virtual) assigned to a wlanX interface.

On read-only file systems, this is not possible, so add some conditional
code to the do_install() to use instead the $DIGI_FAMILY name.

Caveat: if several identical SOMs with read-only-rootfs co-exist on the
same network as APs, they will identify with the same SSID.

Signed-off-by: Hector Palacios <hector.palacios@digi.com>

https://onedigi.atlassian.net/browse/DEL-7708

meta-digi-dey/recipes-connectivity/hostapd/hostapd_%.bbappend

@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2020 Digi International.
+# Copyright (C) 2016-2021 Digi International.
 
 FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
 
@@ -23,6 +23,12 @@ do_install_append() {
 		# Install custom hostapd_IFACE.conf file
 		install -m 0644 ${WORKDIR}/hostapd_wlan1.conf ${D}${sysconfdir}
 	fi
+
+	# Read-only rootfs: actions that substitute postinst script
+	# - append the ${DIGI_FAMILY} string to SSID
+	if [ -n "${@bb.utils.contains('IMAGE_FEATURES', 'read-only-rootfs', '1', '', d)}" ]; then
+		sed -i -e "s,##MAC##,${DIGI_FAMILY},g" ${D}${sysconfdir}/hostapd_wlan?.conf
+	fi
 }
 
 pkg_postinst_ontarget_${PN}() {