The maximum RPC message size was set at 8k for UDP. This is lower

The maximum RPC message size was set at 8k for UDP. This is lower
than the default buffer size in the old RPC code (8800 bytes), and
it could not be overriden by the application. This caused problems
with CFS (/usr/port/security/cfs).

Change this default back to UDPMSGSIZE (8800 bytes), but more
importantly, allow applications to use larger message sizes for
all protocols if desired. Choose an arbitrary maximum message size
of 256k instead of using the default as the maximum (which is
silly).

Reported by:	ache
Reviewed by:	alfred, Martin Blapp <mb@imp.ch>