Preemptive casts ahead of header changes
Detail: The iov_base will be changing from char to void pointer in future, preemptively insert a cast in 'kern_subr.c' to prevent compiler errors. Move svcdebug.h here from TCPIPLibs since its only (private) implementation is this component, and remove unused includes of 'ioc.h' and 'int_hndlr.h'. Admin: Submission for TCP/IP bounty. !NoTag