net/slirp: libslirp 4.9.0 compatibility

net/slirp: libslirp 4.9.0 compatibility

Update the code in net/slirp.c to be compatible with
libslirp 4.9.0, which deprecated slirp_pollfds_fill()
and started using slirp_os_socket type for sockets
(which is a 64-bit integer on win64) for all callbacks
starting with version 6 of the interface.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-ID: <20250130123253.864681-1-mjt@tls.msk.ru>
[thuth: Added some spaces to make checkpatch.pl happy]
Signed-off-by: Thomas Huth <thuth@redhat.com>