Slirp code tries to be smart an avoid data copy by using pointer to
the data. This solution leads to unaligned access, in this case
preq_addr, which is a 32-bit long structure. There is no real point
of avoiding data copy in a such case, as the value itself is smaller
or the same size as a pointer.

The patch replaces pointers to the preq_addr structure by the strcture
itself, and use the address 0.0.0.0 if no address has been requested
(this is not a valid address in such a request). It compares it with
htonl(0L) for correctness reasons, in case a code checker look for such
mistakes. It also uses memcpy() for copying the data, which takes care
of alignement issues.

This fixes an unaligned access on IA64 host while requesting a DHCP
address.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>