bpf, test_run: Fix LIVE_FRAME frame update after a page has been recycled

The test_run code detects whether a page has been modified and
re-initialises the xdp_frame structure if it has, using
xdp_update_frame_from_buff(). However, xdp_update_frame_from_buff()
doesn't touch frame->mem, so that wasn't correctly re-initialised, which
led to the pages from page_pool not being returned correctly. Syzbot
noticed this as a memory leak.

Fix this by also copying the frame->mem structure when re-initialising
the frame, like we do on initialisation of a new page from page_pool.

Fixes: e5995bc7 ("bpf, test_run: fix crashes due to XDP frame overwriting/corruption")
Fixes: b530e9e1 ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN")
Reported-by:  <syzbot+d121e098da06af416d23@syzkaller.appspotmail.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by:  <syzbot+d121e098da06af416d23@syzkaller.appspotmail.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/bpf/20241030-test-run-mem-fix-v1-1-41e88e8cae43@redhat.com