qemu 5.2.0: Add reconnect option support for netdev socket

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1923692
Reported by 'Mark Karpelès' on 2021-04-14 :

Most of qemu socket accepting options (such as chardev) accept among other
things a "reconnect" option.

netdev socket however returns: Invalid parameter 'reconnect'

It would make sense that available options for socket links be at least
partially normalized (also see issue
https://bugs.launchpad.net/qemu/+bug/1903470 which was closed without
resolution).