cmd/utils: enable snap dns discovery

[holiman]

This enables snap sync to find peers via DNS.
Current status:

TRACE[12-03|11:51:00.906] >> FINDNODE/v4                           id=6033ccab352b6a97 addr=52.64.102.159:30303   err=nil
TRACE[12-03|11:51:00.914] Updating DNS discovery root              tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.1:53: no such host"
DEBUG[12-03|11:51:00.914] Error in DNS random node sync            tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.1:53: no such host"
TRACE[12-03|11:51:00.921] Updating DNS discovery root              tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.1:53: no such host"
DEBUG[12-03|11:51:00.921] Error in DNS random node sync            tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.1:53: no such host"
TRACE[12-03|11:51:00.924] Updating DNS discovery root              tree=all.mainnet.ethdisco.net  err=nil
TRACE[12-03|11:51:00.929] Updating DNS discovery root              tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.1:53: no such host"
DEBUG[12-03|11:51:00.929] Error in DNS random node sync            tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.1:53: no such host"
TRACE[12-03|11:51:00.935] DNS discovery lookup                     name=FDXN3SN67NA5DKA4J2GOK7BVQI.all.mainnet.ethdisco.net err=nil

Requires

1. cmd/devp2p: add node filter for snap + fix arg error ethereum/go-ethereum#21950 to filter snap peers from the node list, then
2. add crawling for snap nodes skylenet/discv4-crawl#3 , so it actually publishes it,

[holiman]

Ok, devp2p + crawler updated, snap is now live on ethdisco.net!

[holiman]

@fjl does this look ok to you? some grep from the output of running it

TRACE[12-04|09:42:58.350] DNS discovery lookup                     name=FDXN3SN67NA5DKA4J2GOK7BVQI.all.mainnet.ethdisco.net err=nil
TRACE[12-04|09:42:58.433] DNS discovery lookup                     name=QCZIEBKDK6BL5N6YJLZEPT2RBE.all.mainnet.ethdisco.net err=nil
DEBUG[12-04|09:43:00.407] Couldn't add port mapping                proto=tcp extport=30303 intport=30303 interface="UPnP or NAT-PMP" err="no UPnP or NAT-PMP router discovered"
DEBUG[12-04|09:43:00.407] Couldn't add port mapping                proto=udp extport=30303 intport=30303 interface="UPnP or NAT-PMP" err="no UPnP or NAT-PMP router discovered"
TRACE[12-04|09:43:03.306] Updating DNS discovery root              tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.2:53: dial udp 10.139.1.2:53: i/o timeout"
DEBUG[12-04|09:43:03.306] Error in DNS random node sync            tree=snap.mainnet.ethdisco.net err="lookup snap.mainnet.ethdisco.net on 10.139.1.2:53: dial udp 10.139.1.2:53: i/o timeout"
TRACE[12-04|09:43:03.310] Updating DNS discovery root              tree=snap.mainnet.ethdisco.net err=nil
TRACE[12-04|09:43:03.315] DNS discovery lookup                     name=FDXN3SN67NA5DKA4J2GOK7BVQI.snap.mainnet.ethdisco.net err=nil
TRACE[12-04|09:43:03.321] DNS discovery lookup                     name=3YLFPAIJ5UUQJ2UDJBN23HJBW4.snap.mainnet.ethdisco.net err=nil
TRACE[12-04|09:43:03.328] DNS discovery lookup                     name=UGK3J2JWKYEQJBU6Y32HIQD2KU.snap.mainnet.ethdisco.net err=nil
TRACE[12-04|09:43:03.338] DNS discovery lookup                     name=V4NWX74OBPPFJ7ZPTFWXAXZ5AQ.snap.mainnet.ethdisco.net err=nil
TRACE[12-04|09:43:03.461] DNS discovery lookup                     name=JCQHP47Q2AAFVHNU47K4QPHFQM.all.mainnet.ethdisco.net err=nil

[holiman]

Running this on my machine now, it found the snap-bootnodes pretty quickly

[holiman]

Closing this, I've pushed to the branch instead