[PATCH] wireless/airo: fix setting TX key index plus key in ENCODEEXT

The previous patch that added ENCODEEXT and AUTH support to the airo
driver contained a slight error which would cause setting the TX
key index ignore a valid key-set request at the same time.  This patch
allows any combination of setting the TX key index and setting an
encryption key.

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