package/dhcpdump: fix build without pod2man

Use dhcpdump target to avoid building dhcpdump.8 as it will raise the
following build failure if pod2man is not available:

pod2man --section 8 \
	--date "23 June 2008" \
	--name "DHCPDUMP" \
	--center "User Contributed Software" \
	dhcpdump.pod dhcpdump.8
/bin/sh: pod2man: command not found
make[1]: *** [Makefile:11: dhcpdump.8] Error 127

Fixes:
 - http://autobuild.buildroot.org/results/db3be149ec71de8376f685a6a9f027191d9bccc9

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 698dcb61ea8ab81f92091dba372e996611d1168d)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/dhcpdump/dhcpdump.mk

@@ -20,7 +20,7 @@ DHCPDUMP_CFLAGS = $(TARGET_CFLAGS) -DHAVE_STRSEP
 
 define DHCPDUMP_BUILD_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) CC="$(TARGET_CC) $(DHCPDUMP_CFLAGS) \
-		-D_GNU_SOURCE" LIBS="$(DHCPDUMP_LIBS)"
+		-D_GNU_SOURCE" LIBS="$(DHCPDUMP_LIBS)" dhcpdump
 endef
 
 define DHCPDUMP_INSTALL_TARGET_CMDS