Explicitly link libvirt_net_rpc against SELINUX_LIBS

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

src/Makefile.am

@@ -2232,6 +2232,7 @@ libvirt_net_rpc_la_LDFLAGS = \
 			$(GNUTLS_LIBS) \
 			$(SASL_LIBS) \
 			$(SSH2_LIBS)\
+			$(SELINUX_LIBS) \
 			$(AM_LDFLAGS) \
 			$(CYGWIN_EXTRA_LDFLAGS) \
 			$(MINGW_EXTRA_LDFLAGS)