nx: match_tuple() function now handles nw src/dst

match_tuple() function now handles nw src/dst correctly. FIX:
match_tuple function now handles the nw src/dst masks correctly. If
the mask is not valid, because there is no NX, it will be ignored.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>