nfp: bpf: optimize the adjust_head calls in trivial cases

nfp: bpf: optimize the adjust_head calls in trivial cases

If the program is simple and has only one adjust head call
with constant parameters, we can check that the call will
always succeed at translation time.  We need to track the
location of the call and make sure parameters are always
the same.  We also have to check the parameters against
datapath constraints and ETH_HLEN.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>