sh: Fix ptrace hw_breakpoint handling. Since commit 34d0b5af50a063cded842716633501b38ff815fb it is no longer possible to debug an application using singlestep. The old commit converted singlestep handling via ptrace to hw_breakpoints. The hw_breakpoint is disabled when an event is triggered and not re-enabled again. This patch re-enables the existing hw_breakpoint before the existing breakpoint is reused. Signed-off-by: David Engraf