dco: support float notifications on FreeBSD

dco: support float notifications on FreeBSD

this is a backport of commit b66b80b2ab and 796ad2c559
(squashed, as the second commit undoes quite a bit of #ifdef from the first)

See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=289303 for all
the epic details...

Change-Id: I53e6d1b31c4f673cb646716dce774ef3210f36bd
Signed-off-by: Kristof Provost <kprovost@netgate.com>
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Ralf Lici <ralf@mandelbit.com>
(cherry picked from commit b66b80b2ab73bb422826911b675798e6b789ef03)
(cherry picked from commit 796ad2c55951635382e48ea5b71d13bbb83ebfb1)
Message-Id: <20250908083354.19811-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32827.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>