iproute2: avoid use of implicit declarations

gcc -DLIBDIR=\"/usr/lib64\" -D_GNU_SOURCE -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -Wstrict-prototypes -fPIC -DXT_LIB_DIR=\"/usr/lib64/xtables\" -I../include -DRESOLVE_HOSTNAMES -DLIBDIR=\"/usr/lib64\" -fPIC   -c -o ipx_pton.o ipx_pton.c
In file included from ../include/utils.h:8:0,
                 from ipx_ntop.c:5:
../include/libnetlink.h: In function 'rta_getattr_u64':
../include/libnetlink.h:84:2: warning: implicit declaration of function 'memcpy'
../include/libnetlink.h:84:2: warning: incompatible implicit declaration of built-in function 'memcpy'

include/libnetlink.h

 #ifndef __LIBNETLINK_H__
 #define __LIBNETLINK_H__ 1
 
+#include <string.h>
 #include <asm/types.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>