Updates an existing mobile device by serial number

<mobile_device>
	<general>
		<display_name>iPad</display_name>
		<device_name>iPad</device_name>
		<name>iPad</name>
		<asset_tag>string</asset_tag>
		<serial_number>C02Q7KHTGFWD</serial_number>
		<udid>270aae10800b6e61a2ee2bbc285eb967050b6984</udid>
	</general>
	<location>
		<username>JBetty</username>
		<realname>Betty Jackson</realname>
		<real_name>Betty Jackson</real_name>
		<email_address>[email protected]</email_address>
		<position>Systems Engineer</position>
		<phone>123-555-6789</phone>
		<phone_number>123-555-6789</phone_number>
		<department>Sales Staff</department>
		<building>New York Office</building>
		<room>1159</room>
	</location>
	<purchasing>
		<is_purchased>true</is_purchased>
		<is_leased>true</is_leased>
		<po_number>string</po_number>
		<vendor>string</vendor>
		<applecare_id>string</applecare_id>
		<purchase_price>string</purchase_price>
		<purchasing_account>string</purchasing_account>
		<po_date_epoch>0</po_date_epoch>
		<warranty_expires_epoch>0</warranty_expires_epoch>
		<lease_expires_epoch>0</lease_expires_epoch>
		<life_expectancy>0</life_expectancy>
		<purchasing_contact>string</purchasing_contact>
	</purchasing>
	<extension_attributes>
    <extension_attribute>
		  <id>1</id>
		  <name>Asset Selector</name>
		  <value>Sample Value</value>
    </extension_attribute>
	</extension_attributes>
</mobile_device>