Fix build on Fedora

[mruprich]

I am getting the following error when running the compilation on Fedora Rawhide:

receiver.c: In function ‘find_dstaddr6’:
receiver.c:198:72: error: invalid use of undefined type ‘struct in6_pktinfo’
  198 |                         return &((struct in6_pktinfo *)CMSG_DATA(cmsg))->ipi6_addr;
      |    

The in6_pktinfo is in /usr/include/linux/ipv6.h

[troglobit]

Without even testing your PR, which probably works just fine, I cannot accept it because this is a multi-os project and your patch adds an OS-specific change to the project that would make it importable.

My role here is not a teacher, but ask yourself what would POSIX say about your change, for instance.

[mruprich]

You're right, I realized that shortly after opening the PR. This can be solved by a distribution-specific patch.