vnstat installs a bunch of unneeded x11 dependencies by default using pkgng. those should be trimmed down, or at least it should be possible to avoid instalilng them with a -nox11 binary package.
Over to maintainer.
Over to new maintainer since port r358191.
closing. -nox11 ports are strongly discouraged. it's very easy to provide your own package without GUI option enabled via poudriere if you really don't need libgd and its dependencies.