SOCK: Fix buffer overreach when simplifying IPv4-mapped IPv6 addresses

[markpizz]

 There appears to be a bug in the "_sim_getaddrname" routine

within "sim_sock.c". This code appears:

if (0 == memcmp("::ffff:", hostnamebuf, 7))
memmove(hostnamebuf, 7+hostnamebuf,
strlen(hostnamebuf) + 7 - 1);

The intent is to slide the "hostnamebuf" string seven bytes to the
left to eliminate the "::ffff:" prefix. But it appears to move bytes
from beyond the end of "hostnamebuf".

I believe the last parameter should read "- 7 + 1" instead, as it does
in the earlier "memmove" call within "sim_accept_conn_ex".

Indeed this is a bug.

The negative consequence is very low since it merely picks up some
7 bytes of data past the end of the NUL byte in the existing string which
is likely still within the calling routine's hostnamebuf buffer.

In any case, a slightly clearer fix would be

           strlen(7+hostnamebuf) + 1);

A similar IPv4-mapped to IPb6 address fixup also existed in sim_accept_conn_ex
with the correct length argument has been modified in the same way.