samples: subsys: mgmt: smp_svr: increase fs support stack size
samples: subsys: mgmt: smp_svr: increase fs support stack size

The upload command invokes lfs_stat() on the destination file which
overflows the stack.  Adding 256 bytes seems to make it work.

Signed-off-by: Peter A. Bigot <650538893330be855f76604594b4820eb226769e@pabigot.com>

galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr