libertas: precedence bug

Negate has precedence over comparison so the original test was always
false.  (Neither 0 nor 1 are equal to NL80211_IFTYPE_MONITOR).

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>