Fix mistake in Makefile

packet-exchange/build/Makefile

@@ -6,12 +6,12 @@ SERVER_SRCS  = server.c
 SERVER_SRCS  += recv_packet.c
 SERVER_SRCS  += send_packet.c
 SERVER_SRCS  += utilities.c
+SERVER_SRCS  += xdp_kern.c
 
 CLIENT_SRCS  = client.c
 CLIENT_SRCS += recv_packet.c
 CLIENT_SRCS += send_packet.c
 CLIENT_SRCS += utilities.c
-CLIENT_SRCS += xdp_kern.c
 
 SERVER_OBJS = $(SERVER_SRCS:%.c=%.o)
 CLIENT_OBJS = $(CLIENT_SRCS:%.c=%.o)