Since virnetsocket conditionally uses selinux we need to link against it
otherwise the build fails with:

CCLD     libvirtd
/usr/bin/ld: ../src/.libs/libvirt-lxc.so: undefined reference to symbol 'freecon'
/lib/i386-linux-gnu/libselinux.so.1: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
make[3]: *** [libvirtd] Error 1