rename try_make_readable() to try_make_writable()

In practice this function makes things readable and writable,
so use a less confusing name.

Test: TreeHugger, 'git grep try_make_readable' comes up empty
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I32faad148cc5714cf0ec7246620376ed4dd3d6d2
diff --git a/bpf_progs/clatd.c b/bpf_progs/clatd.c
index 8971f6b..9a9d337 100644
--- a/bpf_progs/clatd.c
+++ b/bpf_progs/clatd.c
@@ -57,7 +57,7 @@
     // Not clear if this is actually necessary considering we use DPA (Direct Packet Access),
     // but we need to make sure we can read the IPv6 header reliably so that we can set
     // skb->mark = 0xDeadC1a7 for packets we fail to offload.
-    try_make_readable(skb, l2_header_size + sizeof(struct ipv6hdr));
+    try_make_writable(skb, l2_header_size + sizeof(struct ipv6hdr));
 
     void* data = (void*)(long)skb->data;
     const void* data_end = (void*)(long)skb->data_end;
@@ -224,7 +224,7 @@
     if (skb->protocol != htons(ETH_P_IP)) return TC_ACT_PIPE;
 
     // Possibly not needed, but for consistency with nat64 up above
-    try_make_readable(skb, sizeof(struct iphdr));
+    try_make_writable(skb, sizeof(struct iphdr));
 
     void* data = (void*)(long)skb->data;
     const void* data_end = (void*)(long)skb->data_end;