Add "generate-only" mode

In this mode bootmac prints the derived MAC value for either Bluetooth
or Wi-Fi, but does not actually configure the hardware.

bootmac

@@ -23,6 +23,7 @@ help_info() {
     echo "bootmac options:"
     echo "    -b | --bluetooth = Configure Bluetooth interface's MAC"
     echo "    -w | --wlan = Configure WLAN interface's MAC"
+    echo "    -g | --generate-only = Generate and print the MAC address to stdout, but do not configure the interface. This option must be specified with either -b or -w, but not both."
     echo ""
     echo "bootmac will configure the MAC addresses for both interfaces if no arguments are passed"
 }
@@ -34,6 +35,11 @@ unknown_option() {
     exit 1
 }
 
+# Set default values for arguments
+WLAN_CONFIGURE_ARG=0
+BLUETOOTH_CONFIGURE_ARG=0
+GENERATE_ONLY_ARG=0
+
 # If no arguments are passed, default to configuring both WLAN and Bluetooth
 if [ "$#" -eq 0 ]; then
     WLAN_CONFIGURE_ARG=1
@@ -41,7 +47,7 @@ if [ "$#" -eq 0 ]; then
 fi
 
 # Use the "getopts" built-in to parse arguments
-while getopts bwh-: arg; do
+while getopts bwhg-: arg; do
     case "$arg" in
         w)
             WLAN_CONFIGURE_ARG=1
@@ -49,6 +55,9 @@ while getopts bwh-: arg; do
         b)
             BLUETOOTH_CONFIGURE_ARG=1
             ;;
+        g)
+            GENERATE_ONLY_ARG=1
+            ;;
         h)
             help_info
             exit 0
@@ -61,6 +70,9 @@ while getopts bwh-: arg; do
                 bluetooth)
                     BLUETOOTH_CONFIGURE_ARG=1
                     ;;
+                generate-only)
+                    GENERATE_ONLY_ARG=1
+                    ;;
                 help)
                     help_info
                     exit 0
@@ -81,6 +93,14 @@ if [ "$((OPTIND-1))" != "$#" ]; then
     unknown_option
 fi
 
+# If "generate-only" is specified, either Wi-Fi or Bluetooth must be requested, but not both
+if [ "$GENERATE_ONLY_ARG" = 1 ] && [ "$((WLAN_CONFIGURE_ARG+BLUETOOTH_CONFIGURE_ARG))" != 1 ]; then
+    echo "ERROR: Either Wi-Fi or Bluetooth must be requested together with --generate-only." >&2
+    echo "" >&2
+    help_info
+    exit 1
+fi
+
 mac_generate() {
     # Try to retrieve the serial number from the cmdline
     log "retrieving device serial number"
@@ -150,6 +170,15 @@ mac_wlan() {
 
 mac_generate
 
+if [ "$GENERATE_ONLY_ARG" = 1 ]; then
+    if [ "$WLAN_CONFIGURE_ARG" = 1 ]; then
+        echo "$WLAN_MAC"
+    elif [ "$BLUETOOTH_CONFIGURE_ARG" = 1 ]; then
+        echo "$BT_MAC"
+    fi
+    exit 0
+fi
+
 if [ "$WLAN_CONFIGURE_ARG" = 1 ]; then
     log "Configuring MAC address for WLAN"
     mac_wlan