Problem : "Install Virtualbox ose additions (with fix kernel src)"

Solve :
- Run cd /usr/ports/emulators/virtualbox-ose-additions && make install clean

ONLY IF YOU DON'T HAVE KERNEL SOURCES

- You need the kernel sources for compile, run fetch ftp://ftp.freebsd.org/pub/FreeBSD/releases/amd64/11.0-RELEASE/src.txz
- And place the sources with tar -C / -xvzf src.txz

AFTER INSTALL
- Add these lines to /etc/rc.conf :
vboxguest_enable="YES"
vboxservice_enable="YES"