bubblewrap misuses CMSG_DATA() macro

[mcatanzaro]

cmsg(3) says:

       CMSG_DATA()
              returns  a pointer to the data portion of a cmsghdr.  The pointer returned cannot be assumed to be suitably aligned for accessing arbitrary
              payload data types.  Applications should not cast it to a pointer type matching the payload, but should instead use memcpy(3) to copy  data
              to or from a suitably declared object.

send_pid_on_socket() and read_pid_from_socket() in bubblewrap's utils.c both cast the return value exactly like the documentation says not to do.

(This should be a very easy newcomers issue.)

[mcatanzaro]

Separately, it looks like the msg_control and msg_controllen fields are also supposed to be aligned. cmsg(3) shows this example:

           union {         /* Ancillary data buffer, wrapped in a union
                              in order to ensure it is suitably aligned */
               char buf[CMSG_SPACE(sizeof(myfds))];
               struct cmsghdr align;
           } u;

           msg.msg_iov = &io;
           msg.msg_iovlen = 1;
           msg.msg_control = u.buf;
           msg.msg_controllen = sizeof(u.buf);