First and foremost the fix for XSA-270. On top of that further changes
which looked desirable to me while investigating that XSA.
1: fix input validation in xenvif_set_hash_mapping()
2: validate queue numbers in xenvif_set_hash_mapping()
3: handle page straddling in xenvif_set_hash_mapping()
Signed-off-by: Jan Beulich <redacted>