ifconfig(8) now supports some output formatting options

ifconfig(8) now supports some output formatting options

specified by the -f flag or IFCONFIG_FORMAT environment variable, the user
can request that inet4 subnet masks be printed in CIDR or dotted-quad
notation, in addition to the traditional hex output.
inet6 prefixes can be printed in CIDR as well.

For more documentation see the ifconfig(8) man page.

PR:		169072
Requested by:	seanc, marcel, brd, many others
Reviewed by:	gnn, jhb (earlier version)
Relnotes:	yes
Sponsored by:	ScaleEngine Inc.
Differential Revision:	https://reviews.freebsd.org/D2856