ss: Replace printf() calls for "main" output by calls to helper

ss: Replace printf() calls for "main" output by calls to helper

This is preparation work for output buffering, which will allow
us to use optimal spacing and alignment of logical "columns".

The new out() function is just a re-implementation of a typical
libc's printf(), except that the return value of vfprintf() is
ignored as no callers use it. This implementation will be
replaced in the next patches to provide column width adjustment
and adequate spacing.

All printf() calls that output parts of the socket list are now
replaced by calls to out(). Output of summary and version is
excluded from this.

No functional differences here, output not affected.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>