comms/ser2net: update to 4.6.4 and take maintainership

Changelog: https://sourceforge.net/p/ser2net/news

Major changes since 3.5.1 (2017)

• massive rewrite of ser2net
• Configuration has been converted over to use YAML
• supports encrypted and authenticated connections using gensio gtlssh
• ability to "connect back" to a remote address data comes in on a device
• new gensio dependency to manage data streams, SSL, TELNET and so
• add mDNS support
• DSR/RTS line controls on the serialdev gensio
• 2-factor authentication support to gtlssh
• use PAM passwords to authenticate ser2net connections
• ed25519 end elliptical key support for gtlssh and certauth
• ratelimit - limit the data throughput on the write side of the gensio stack
• AFSK modem gensio has been added to implements the 1200 baud modem used for AX.25 in ham radio

This version breaks the existing ser2net configuration who has to be
converted over using YAML. Please see the examples on ser2net.yaml sample
configuration and read the ser2net.yaml manpage on how to configure
the new version. Additional links and resources have been provided on the
pkg-message.