slirp: Don't mark struct ipq or struct ipasfrag as packed

slirp: Don't mark struct ipq or struct ipasfrag as packed

There is no reason to mark the struct ipq and struct ipasfrag as
packed: they are naturally aligned anyway, and are not representing
any on-the-wire packet format.  Indeed they vary in size depending on
the size of pointers on the host system, because the 'struct qlink'
members include 'void *' fields.

Dropping the 'packed' annotation fixes clang -Waddress-of-packed-member
warnings and probably lets the compiler generate better code too.

The only thing we do care about in the layout of the struct is
that the frag_link matches up with the ipf_link of the struct
ipasfrag, as documented in the comment on that struct; assert
at build time that this is the case.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>