Replace int status/reason_code with u16 variable

Replace int status/reason_code with u16 variable

These cases are for the IEEE 802.11 Status Code and Reason Code and
those fields are unsigned 16 bit values, so use the more appropriate
type consistently. This is mainly to document the uses and to make the
source code easier to understand.

Signed-off-by: Jouni Malinen <j@w1.fi>