Revert "Remove momdemmanager"

This reverts commit 48dcdfa417.

modemmanager/README.md

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+# OpenWrt ModemManager
+
+## Description
+
+Cellular modem control and connectivity
+
+Optional libraries libmbim and libqmi are available.
+Your modem may require additional kernel modules and/or the usb-modeswitch
+package.
+
+## Usage
+
+Once installed, you can configure the 2G/3G/4G modem connections directly in
+/etc/config/network as in the following example:
+
+    config interface 'broadband'
+        option device      '/sys/devices/platform/soc/20980000.usb/usb1/1-1/1-1.2/1-1.2.1'
+        option proto       'modemmanager'
+        option apn         'ac.vodafone.es'
+        option allowedauth 'pap chap'
+        option username    'vodafone'
+        option password    'vodafone'
+        option pincode     '7423'
+        option iptype      'ipv4'
+        option lowpower    '1'
+        option signalrate  '30'
+
+Only 'device' and 'proto' are mandatory options, the remaining ones are all
+optional.
+
+The 'allowedauth' option allows limiting the list of authentication protocols.
+It is given as a space-separated list of values, including any of the
+following: 'pap', 'chap', 'mschap', 'mschapv2' or 'eap'. It will default to
+allowing all protocols.
+
+The 'iptype' option supports any of these values: 'ipv4', 'ipv6' or 'ipv4v6'.
+It will default to 'ipv4' if not given.
+
+The 'signalrate' option set's the signal refresh rate (in seconds) for the device.
+You can call signal info with command: mmcli -m 0 --signal-get