[Buildroot] package/conmon: broken by recent change removing dlfcn.h

[Christian Stewart]

Hi Waldemar, Thomas,

A recent commit added a patch removing dlfcn.h:

https://lore.kernel.org/buildroot/ZNdpt%2FgB95HIWDAq@waldemar-brodkorb.de/

This header is needed for RTLD_NOW and causes "RTLD_NOW is not
defined" type build errors when building for a Raspberry Pi 4.

Please revert that commit / remove that patch or otherwise fix the
undefined symbol.

Thank you,
Christian Stewart