networking: consolidate the IP checksum code. -129 bytes.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/Kbuild.src b/libbb/Kbuild.src
index 875d024..335b341 100644
--- a/libbb/Kbuild.src
+++ b/libbb/Kbuild.src
@@ -166,6 +166,12 @@
 lib-$(CONFIG_MPSTAT) += get_cpu_count.o
 lib-$(CONFIG_POWERTOP) += get_cpu_count.o
 
+lib-$(CONFIG_PING) += inet_cksum.o
+lib-$(CONFIG_TRACEROUTE) += inet_cksum.o
+lib-$(CONFIG_TRACEROUTE6) += inet_cksum.o
+lib-$(CONFIG_UDHCPC) += inet_cksum.o
+lib-$(CONFIG_UDHCPD) += inet_cksum.o
+
 # We shouldn't build xregcomp.c if we don't need it - this ensures we don't
 # require regex.h to be in the include dir even if we don't need it thereby
 # allowing us to build busybox even if uclibc regex support is disabled.