Fix driver_bsd.c build

Fix driver_bsd.c build

On NetBSD 5.0.1, driver_bsd.c build fails with message below.

../src/drivers/driver_bsd.c: In function 'wpa_driver_bsd_associate':
../src/drivers/driver_bsd.c:1170: warning: implicit declaration of function 'wpa_driver_bsd_set_auth_alg'
../src/drivers/driver_bsd.c: At top level:
../src/drivers/driver_bsd.c:1204: error: static declaration of 'wpa_driver_bsd_set_auth_alg' follows non-static declaration
../src/drivers/driver_bsd.c:1170: error: previous implicit declaration of 'wpa_driver_bsd_set_auth_alg' was here
gmake: *** [../src/drivers/driver_bsd.o] Error 1

This patch solves this issue.