Fixed wrong bitmask in status register in user_exc_enter() (#78)
Fixed wrong bitmask in status register in user_exc_enter() (#78)

The status register SR_KSU bits are: 0 for kernel, 1 for supervisor, 2 for user
Before this commit, user_exc_enter() 'turned off' the kernel-mode-bits instead of the non-kernel-mode-bits
cahirwpz/mimiker,cahirwpz/mimiker,dyniec/mimiker,rafalcieslak/mimiker,czapiga/mimiker,czapiga/mimiker,dyniec/mimiker,dyniec/mimiker,cahirwpz/wifire-os,rafalcieslak/mimiker,czapiga/mimiker,rafalcieslak/mimiker,dyniec/mimiker,cahirwpz/mimiker,rafalcieslak/mimiker,cahirwpz/mimiker,czapiga/mimiker