package/dhcp: install shared libraries

package/dhcp: install shared libraries

We don't use "make install" for target installation because we build all
utilities (server, relay, client) but install only the selected ones.

The utilities, however, require the shared libraries to work, so use the
"install-exec" make target to install them. This also installs static
libraries but they are removed later by target-finalize.

With this change the omshell utility is installed if server is selected.
We keep it, since it is small and may be useful at run-time.

Fixes:
  https://bugs.busybox.net/show_bug.cgi?id=12086

Signed-off-by: Carlos Santos <unixmania@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>