alx: fix implicit-function-declaration build errors

Fixes build breakage in Ubuntu PPC build, e.g.:

    alx_main.c: error: implicit declaration of function ‘vzalloc’ [-Werror=implicit-function-declaration]

Signer-off-by: Kamal Mostafa <kamal@canonical.com>
diff --git a/src/alx_main.c b/src/alx_main.c
index 959920f..7686aec 100644
--- a/src/alx_main.c
+++ b/src/alx_main.c
@@ -26,6 +26,8 @@
 #include <linux/bitops.h>
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
+#include <linux/vmalloc.h>
+#include <net/ip6_checksum.h>
 
 #include "alx_reg.h"
 #include "alx_hw.h"