Do not fill screen, while muted.

Sponsored by:	The FreeBSD Foundation
Loosen the processing of *_IF_aliasN vars to be less strict. Previously,
the first alias had to be _alias0 and processing stopped at the first non-
defined variable (preventing gaps). Allowing gaps gives the administrator
the ability to group aliases in an adhoc manner and also lifts the
requirement to renumber aliases simply to comment-out an existing one.
Aliases are processed in numerical ascending order.

Discussed on:	-rc
MFC after:	1 week