drop htonl(), htons(), ntohl(), ntohs() MD functions from libc

drop htonl(), htons(), ntohl(), ntohs() MD functions from libc

Userland code compiled in a normal fashion picks up the htonl(),
htons(), ntohl(), ntohs() macros implemented by endian.h.  The
functions in libc are effectively unused.  Keep the MI functions
in case something looks for the symbols in libc or plays games
with #undef, but change them to wrap the implementation from
endian.h.

tweaks suggested by claudio@, ok miod@