When accessing the length field of an ipv6_header a byte order switch (host -> network) is necessary.
Otherwise, it breaks calculations or the checksum and other tcp related computations.
Furthermore, when writing to ipv6_header->length it is important to switch this
from host byte order to network byte order.
send_tcp returns either the length of the sent data,
or -1, if an error was detected.
The current implementation checks for != 1.
This results in executing the error case, although
there was semantically no error returned from send_tcp.
get_socket(i) returns NULL, when no specific socket is found.
Without an appropriate check for NULL, the current state
of the code leads to a segfault.
destiny: added parens
destiny: continuing the loop makes more sense than returning at first sight of NULL
