build: fix error when running `configure --disable-doc`
build: fix error when running `configure --disable-doc`

Signed-off-by: Thomas Haller <16e26612e4159990a6b3691e92592e691ff74132@redhat.com>

congwang/libnl,HolyShitMan/libnl-1,baloo/libnl,UnicronNL/libnl3,claudelee/libnl,baloo/libnl,kolyshkin/libnl,tklauser/libnl,cfriedt/libnl,cyclops8456/libnl3,kolyshkin/libnl,claudelee/libnl,houstar/libnl,claudelee/libnl,congwang/libnl,kolyshkin/libnl,honsys/libnl,vyos/libnl3,greearb/libnl-ct,tgraf/libnl,cfriedt/libnl,UnicronNL/libnl3,baloo/libnl,dsahern/libnl,houstar/libnl,tgraf/libnl,honsys/libnl,UnicronNL/libnl3,congwang/libnl,mshirley/libnl,baloo/libnl,houstar/libnl,UnicronNL/libnl3,tklauser/libnl,cyclops8456/libnl3,vyos/libnl3,honsys/libnl,HolyShitMan/libnl-1,thom311/libnl,vyos/libnl3,tgraf/libnl,tgraf/libnl,vyos/libnl3,tklauser/libnl,HolyShitMan/libnl-1,greearb/libnl-ct,dsahern/libnl,congwang/libnl,thom311/libnl,mshirley/libnl,cfriedt/libnl,greearb/libnl-ct,thom311/libnl,dsahern/libnl,tklauser/libnl,cfriedt/libnl,cyclops8456/libnl3,dsahern/libnl,HolyShitMan/libnl-1,kolyshkin/libnl,mshirley/libnl,honsys/libnl,claudelee/libnl,cyclops8456/libnl3,mshirley/libnl,houstar/libnl