refactor: replace RecursiveMutex m_addr_fetches_mutex with Mutex
refactor: replace RecursiveMutex m_addr_fetches_mutex with Mutex

The RecursiveMutex m_addr_fetches_mutex is used at three places:
    - CConnman::AddAddrFetch()
    - CConnman::ProcessAddrFetch()
    - CConnman::ThreadOpenConnections()
In each of the critical sections, only the the m_addr_fetches is accessed
(and in the last case, also vAddedNodes), without any chance that within
one section another one is called. Hence, we can use an ordinary Mutex
instead of RecursiveMutex.

dscotese/bitcoin,sstone/bitcoin,domob1812/bitcoin,jamesob/bitcoin,namecoin/namecore,pataquets/namecoin-core,sipsorcery/bitcoin,lateminer/bitcoin,andreaskern/bitcoin,GroestlCoin/bitcoin,bitcoinsSG/bitcoin,bitcoinknots/bitcoin,tecnovert/particl-core,particl/particl-core,bitcoin/bitcoin,Xekyo/bitcoin,jlopp/statoshi,namecoin/namecore,jlopp/statoshi,dscotese/bitcoin,domob1812/bitcoin,lateminer/bitcoin,jamesob/bitcoin,domob1812/namecore,lateminer/bitcoin,sipsorcery/bitcoin,instagibbs/bitcoin,lateminer/bitcoin,GroestlCoin/GroestlCoin,fanquake/bitcoin,ajtowns/bitcoin,namecoin/namecore,andreaskern/bitcoin,andreaskern/bitcoin,fanquake/bitcoin,jlopp/statoshi,Xekyo/bitcoin,achow101/bitcoin,anditto/bitcoin,domob1812/namecore,jlopp/statoshi,sipsorcery/bitcoin,mruddy/bitcoin,bitcoinsSG/bitcoin,jamesob/bitcoin,mm-s/bitcoin,ajtowns/bitcoin,tecnovert/particl-core,anditto/bitcoin,sstone/bitcoin,mruddy/bitcoin,instagibbs/bitcoin,mm-s/bitcoin,Xekyo/bitcoin,anditto/bitcoin,mruddy/bitcoin,ajtowns/bitcoin,AkioNak/bitcoin,domob1812/bitcoin,GroestlCoin/GroestlCoin,mm-s/bitcoin,namecoin/namecoin-core,GroestlCoin/bitcoin,lateminer/bitcoin,mm-s/bitcoin,sstone/bitcoin,kallewoof/bitcoin,kallewoof/bitcoin,lateminer/bitcoin,bitcoinknots/bitcoin,dscotese/bitcoin,particl/particl-core,jlopp/statoshi,bitcoinsSG/bitcoin,domob1812/namecore,kallewoof/bitcoin,AkioNak/bitcoin,achow101/bitcoin,jambolo/bitcoin,jambolo/bitcoin,Xekyo/bitcoin,tecnovert/particl-core,anditto/bitcoin,mm-s/bitcoin,namecoin/namecoin-core,jambolo/bitcoin,particl/particl-core,GroestlCoin/GroestlCoin,GroestlCoin/GroestlCoin,pataquets/namecoin-core,bitcoin/bitcoin,instagibbs/bitcoin,AkioNak/bitcoin,mruddy/bitcoin,sstone/bitcoin,bitcoinknots/bitcoin,ajtowns/bitcoin,GroestlCoin/bitcoin,bitcoinsSG/bitcoin,fujicoin/fujicoin,bitcoin/bitcoin,bitcoinknots/bitcoin,jambolo/bitcoin,jamesob/bitcoin,namecoin/namecoin-core,fujicoin/fujicoin,kallewoof/bitcoin,AkioNak/bitcoin,andreaskern/bitcoin,pataquets/namecoin-core,AkioNak/bitcoin,kallewoof/bitcoin,ajtowns/bitcoin,instagibbs/bitcoin,andreaskern/bitcoin,GroestlCoin/bitcoin,pataquets/namecoin-core,GroestlCoin/GroestlCoin,fanquake/bitcoin,tecnovert/particl-core,namecoin/namecore,tecnovert/particl-core,GroestlCoin/bitcoin,mruddy/bitcoin,dscotese/bitcoin,achow101/bitcoin,namecoin/namecore,Xekyo/bitcoin,domob1812/namecore,sipsorcery/bitcoin,domob1812/bitcoin,GroestlCoin/GroestlCoin,achow101/bitcoin,pataquets/namecoin-core,jlopp/statoshi,mm-s/bitcoin,domob1812/bitcoin,instagibbs/bitcoin,achow101/bitcoin,jambolo/bitcoin,andreaskern/bitcoin,bitcoin/bitcoin,GroestlCoin/bitcoin,sipsorcery/bitcoin,domob1812/namecore,bitcoinknots/bitcoin,fujicoin/fujicoin,ajtowns/bitcoin,fanquake/bitcoin,domob1812/bitcoin,particl/particl-core,AkioNak/bitcoin,achow101/bitcoin,namecoin/namecoin-core,fujicoin/fujicoin,sipsorcery/bitcoin,fanquake/bitcoin,bitcoinsSG/bitcoin,mruddy/bitcoin,dscotese/bitcoin,dscotese/bitcoin,fanquake/bitcoin,namecoin/namecore,bitcoin/bitcoin,anditto/bitcoin,pataquets/namecoin-core,fujicoin/fujicoin,instagibbs/bitcoin,sstone/bitcoin,fujicoin/fujicoin,Xekyo/bitcoin,tecnovert/particl-core,anditto/bitcoin,particl/particl-core,namecoin/namecoin-core,sstone/bitcoin,jamesob/bitcoin,jambolo/bitcoin,domob1812/namecore,namecoin/namecoin-core,bitcoinsSG/bitcoin,kallewoof/bitcoin,bitcoin/bitcoin,particl/particl-core,jamesob/bitcoin