Use uint8_t not char for binary data to avoid -Wall -Werror issues on x86 builds

Change-Id: Ib61e67f15360c27c3ebf61f870a9482217c52357
diff --git a/ipv6.c b/ipv6.c
index 2e83be1..d519e1b 100644
--- a/ipv6.c
+++ b/ipv6.c
@@ -35,7 +35,7 @@
  * returns: the highest position in the output clat_packet that's filled in
  */
 int icmp6_packet(clat_packet out, int pos, const struct icmp6_hdr *icmp6, size_t len) {
-  const char *payload;
+  const uint8_t *payload;
   size_t payload_size;
 
   if(len < sizeof(struct icmp6_hdr)) {
@@ -43,7 +43,7 @@
     return 0;
   }
 
-  payload = (const char *) (icmp6 + 1);
+  payload = (const uint8_t *) (icmp6 + 1);
   payload_size = len - sizeof(struct icmp6_hdr);
 
   return icmp6_to_icmp(out, pos, icmp6, payload, payload_size);
@@ -74,12 +74,12 @@
  * len    - size of packet
  * returns: the highest position in the output clat_packet that's filled in
  */
-int ipv6_packet(clat_packet out, int pos, const char *packet, size_t len) {
+int ipv6_packet(clat_packet out, int pos, const uint8_t *packet, size_t len) {
   const struct ip6_hdr *ip6 = (struct ip6_hdr *) packet;
   struct iphdr *ip_targ = (struct iphdr *) out[pos].iov_base;
   struct ip6_frag *frag_hdr = NULL;
   uint8_t protocol;
-  const char *next_header;
+  const uint8_t *next_header;
   size_t len_left;
   uint32_t old_sum, new_sum;
   int iov_len;