You can think of the API as being defined in <ldap.h> and the ABI being defined as the linker's interface. In both cases, the interface is not just syntax, but also semantics associated with the syntax.
to /usr/lib/liblber.so.2 ?so that it would be very bad to link (ln -s) /usr/lib/liblber-2.2.so.7.0.1
It certainly would not be all that wise.
Ciao, Michael.