[BusyBox] BUG 0.51 mount /etc/mtab

[Magnus Damm]

> I don't know the right solution (affecting Hurd and others),
> but changing BB_MTAB to BB_FEATURE_MOUNT_MTAB_SUPPORT in
                          ^
Copy and paste error. 
In 0.51 it should be BB_FEATURE_MTAB_SUPPORT.

/ Magnus