Our implementation has restriction on stack pointers for function
calls.  Move the common checks into a helper for reuse.  The state
has to be encapsulated into a structure to support parameters
other than BPF_REG_2.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: NQuentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: NJiong Wang <jiong.wang@netronome.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>