vty: use install_lib_element() and install_lib_element_ve()

See https://lists.osmocom.org/pipermail/openbsc/2020-October/013278.html.

Change-Id: I0eff9e0daa1c4327fec8034755986d768f9ba511
Depends: I8baf31ace93c536421893c2aa4e3d9d298dcbcc6
Related: SYS#4937
1 file changed