evaluate: insert byte-order conversions for expressions between 9 and 15 bits

evaluate: insert byte-order conversions for expressions between 9 and 15 bits

Round up expression lengths when determining whether to insert a
byte-order conversion.  For example, if one is masking a network header
which spans a byte boundary, the mask will span two bytes and so it will
need to be in NBO.

Fixes: bb03cbcd18a1 ("evaluate: no need to swap byte-order for values of fewer than 16 bits.")
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>