configure: Add libraries for qemu-ga on Solaris

Move socket-related Solaris libraries to $solarisnetlibs and use them
for both $LIBS and $libs_qga.

Fixes build on illumos without --disable-guest-agent.
Signed-off-by: NLee Essen <lee.essen@nowonline.co.uk>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

configure

@@ -468,7 +468,9 @@ SunOS)
 # needed for TIOCWIN* defines in termios.h
   QEMU_CFLAGS="-D__EXTENSIONS__ $QEMU_CFLAGS"
   QEMU_CFLAGS="-std=gnu99 $QEMU_CFLAGS"
-  LIBS="-lsocket -lnsl -lresolv $LIBS"
+  solarisnetlibs="-lsocket -lnsl -lresolv"
+  LIBS="$solarisnetlibs $LIBS"
+  libs_qga="$solarisnetlibs $libs_qga"
 ;;
 AIX)
   aix="yes"