package/syslog-ng: depend on !BR2_STATIC_LIBS

Upstream now unconditionally requires dlfcn.h:
- https://github.com/balabit/syslog-ng/commit/01258e56abc5804f8ea977ff9ab98cc8e2fd4702

Fixes:
- http://autobuild.buildroot.net/results/c0bca852e053cd0e021205b3a949e750ae602333



Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Carlos Santos <casantos@datacom.com.br>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>