Add -R to netstat to dump RSS/flow information.

This is intended to help in diagnostics and debugging of NIC and stack
flowid support.

Eventually this will grow another column (RSS CPU ID) but
that currently isn't cached in the inpcb.

There's also no clean flowtype -> flowtype identifier string.  This is
the mbuf M_HASHTYPE_* values for RSS.

Here's some example output:

adrian@adrian-hackbox:~/work/freebsd/head/src % netstat -Rn | more
Active Internet connections
Proto Recv-Q Send-Q Local Address          Foreign Address           flowid ftype
tcp4       0      0 10.11.1.65.22          10.11.1.64.12409        29041942     2
udp4       0      0 127.0.0.1.123          *.*                     00000000     0
udp6       0      0 fe80::1%lo0.123        *.*                     00000000     0
udp6       0      0 ::1.123                *.*                     00000000     0
udp4       0      0 10.11.1.65.123         *.*                     00000000     0

Tested:

* amd64 system w/ igb NIC; local driver changes to expose RSS flowid in if_igb.