Code:
#awk '/^<\/.*>$/{print $0",";next}{printf $0","}END{printf "\n"}' testtag
<?xml version="1.0" encoding="UTF-8"?>,<identifier>1234567890</identifier>,,<tag>,<ntype>multi</ntype>,<mobileSubscriberType>genericSubscriber</mobileSubscriberType>,<umtsSubscriber>,<accTypeGSM>true</accTypeGSM>,<accTypeGERAN>true</accTypeGERAN>,<accTypeUTRAN>true</accTypeUTRAN>,</umtsSubscriber>,
<wllSubscriber>false</wllSubscriber>,<mscat>10</mscat>,<odboc>0</odboc>,<odbic>0</odbic>,<odbr>0</odbr>,<odboprc>0</odboprc>,<odbssm>0</odbssm>,<clip>true</clip>,<clipOverride>false</clipOverride>,<colpOverride>false</colpOverride>,<hold>true</hold>,<mpty>true</mpty>,<nwa>3</nwa>,<odbgprs>0</odbgprs>,<rr>WhiteL</rr>,<sr>2</sr>,<odbsci>0</odbsci>,<ts11>,<msisdn>12345</msisdn>,<bcieID>TELEPHON</bcieID>,</ts11>,
<ts21>,<msisdn>12345</msisdn>,</ts21>,
<ts22>,<msisdn>12345</msisdn>,</ts22>,
<bs30genr>,<msisdn>12345</msisdn>,<bcieID>VIDEO</bcieID>,</bs30genr>,
<gprs>,<msisdn>12345</msisdn>,</gprs>,
<cfu>,<basicServiceGroup>TS10-telephony</basicServiceGroup>,<status>4</status>,<notifyCallingSubscriber>false</notifyCallingSubscriber>,</cfu>,
<cfu>,<basicServiceGroup>BS30-dataSync</basicServiceGroup>,<status>4</status>,<notifyCallingSubscriber>false</notifyCallingSubscriber>,</cfu>,
<cfb>,<basicServiceGroup>TS10-telephony</basicServiceGroup>,<isdnNumber>1234567</isdnNumber>,<status>7</status>,<notifyCallingSubscriber>false</notifyCallingSubscriber>,<notifyForwardingSubscriber>false</notifyForwardingSubscriber>,<ftnoType>internat</ftnoType>,</cfb>,