network: don't let _maintain_sessions die from CancelledError
network: don't let _maintain_sessions die from CancelledError

as then the network would get paralysed and no one can fix it

neocogent/electrum,pooler/electrum-ltc,spesmilo/electrum,vialectrum/vialectrum,pooler/electrum-ltc,neocogent/electrum,pooler/electrum-ltc,vialectrum/vialectrum,spesmilo/electrum,wakiyamap/electrum-mona,pooler/electrum-ltc,fujicoin/electrum-fjc,vialectrum/vialectrum,spesmilo/electrum,fujicoin/electrum-fjc,fujicoin/electrum-fjc,wakiyamap/electrum-mona,wakiyamap/electrum-mona,neocogent/electrum,spesmilo/electrum,wakiyamap/electrum-mona