bpf: Clear packet pointers after changing packet data in kfuncs

bpf_xdp_pull_data() may change packet data and therefore packet pointers
need to be invalidated. Add bpf_xdp_pull_data() to the special kfunc
list instead of introducing a new KF_ flag until there are more kfuncs
changing packet data.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250922233356.3356453-5-ameryhung@gmail.com