Print error when write() to tun device fails.
Print error when write() to tun device fails.

This happens on OpenBSD when writing IPv6 packets, for some reason.
Silent failure is not recommended; much better to bitch about it.

Signed-off-by: David Woodhouse <b460d66aaf00c296a3db1c1d9eeafc081d5f7d70@intel.com>

don-johnny/openconnect,certik/openconnect,atyndall/openconnect,sihde/openconnect,lins05/openconnect,chadcatlett/openconnect,cernekee/openconnect,lins05/openconnect,atyndall/openconnect,chadcatlett/openconnect,mdutton3/OpenConnect,brandt/openconnect,mtmiller/openconnect,matlockx/openconnect,nmav/openconnect-mine,don-johnny/openconnect,nmav/openconnect-mine,brandt/openconnect,nmav/openconnect-mine,liiir1985/openconnect,mdutton3/OpenConnect,chadcatlett/openconnect,matlockx/openconnect,certik/openconnect,mveplus/openconnect-client,atyndall/openconnect,liiir1985/openconnect,mtmiller/openconnect,mveplus/openconnect-client,neshema/openconnect,neshema/openconnect,don-johnny/openconnect,cernekee/openconnect,mdutton3/OpenConnect,lins05/openconnect,cernekee/openconnect,mtmiller/openconnect,sihde/openconnect,matlockx/openconnect,matlockx/openconnect,neshema/openconnect,certik/openconnect,cernekee/openconnect,brandt/openconnect,nmav/openconnect-mine,atyndall/openconnect,don-johnny/openconnect,mveplus/openconnect-client,sihde/openconnect,mveplus/openconnect-client,liiir1985/openconnect,chadcatlett/openconnect,liiir1985/openconnect,lins05/openconnect,neshema/openconnect,brandt/openconnect,mtmiller/openconnect