Increase the defaults for the maximum socket buffer limit,

Increase the defaults for the maximum socket buffer limit,
and the maximum TCP send and receive buffer limits from 256kB
to 2MB.

For sb_max_adj we need to add the cast as already used in the sysctl
handler to not overflow the type doing the maths.

Note that this is just the defaults.  They will allow more memory
to be consumed per socket/connection if needed but not change the
default "idle" memory consumption.   All values are still tunable
by sysctls.

Suggested by:	gnn
Discussed on:	arch (Mar and Aug 2011)
MFC after:	3 weeks
Approved by:	re (kib)