Fix compile error for in6_ifreq define changes

[madafoo]

After my debian sid upgrade the latest linux-libc-dev from 4.9.30 to 4.11.6, it break the compile for in6_ifreq changes. Please help me verify the changes on different platform to make sure it do not break anything elese.

[cjdelisle]

Does it hurt to say:

#if !defined(_LINUX_IN6_H) && !defined(_UAPI_LINUX_IN6_H) && !defined(_IPV6_H) && !defined(_UAPI_IPV6_H)
.....

instead ?

[madafoo]

In fact, old code
#if !defined(_LINUX_IN6_H) && !defined(_UAPI_LINUX_IN6_H)
is complete wrong, it is always be true.
I have look deep in the difference between linux-libc-dev 4.11.6 and 4.9.30 caused the problem is the change of /usr/include/linux/ipv6_route.h:

@@ -14,6 +14,7 @@
#define _LINUX_IPV6_ROUTE_H

#include <linux/types.h>
+#include <linux/in6.h> /* For struct in6_addr. */

#define RTF_DEFAULT 0x00010000 /* default - learned via ND /
#define RTF_ALLONLINK 0x00020000 / (deprecated and will be removed)`

[madafoo]

torvalds/linux@6c07ec0

The ipv6_route.h changes was brought into kernel about 4 month ago.

[cjdelisle]

Hmm, the old code was there because it fixed a problem at that time so it cannot have been completely wrong. How about we make a solution which is guaranteed to fix it by changing the name to struct Cjdns_in6_ifreq so it will never collide. Then we can drop the stupid ifdef entirely.

[madafoo]

In fact, before 8efff0c#diff-014ec6296bbbd370c5bdfaa6bf461503L45 the code is still use the ipv6.h, and as the comment said:

We need to pull in linux/ipv6.h for in6_ifreq but a bunch
of structures are defined in in6.h and also in in.h causing
errors from redefinition.

[cjdelisle]

efd7d7f should close this

[vikulin]

See details in hyperboria/android#72:

Replace 7 years old NACL library to modern libsodium.
https://github.com/jedisct1/libsodium