Fix -4/-6 flag being ignored when no specific test is selected

set_scanning_defaults() reset do_ipv4_only/do_ipv6_only to false. When
no individual test is requested on the command line, count_do_variables
returns 0 and parse_cmd_line() calls set_scanning_defaults() to enable
the standard test suite, which silently wiped out the user's -4/-6
selection. As a result determine_ip_addresses() fell through to its
"scan everything" branch and scanned both the A and AAAA records,
producing one scanResult per IP.

The IP-version flags are connection options, not test-selection state,
and are already initialized in initialize_globals(), so remove the
stray resets from set_scanning_defaults().

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: SteveVaneeckhout

testssl.sh

@@ -24574,9 +24574,6 @@ set_scanning_defaults() {
           VULN_COUNT=14
      fi
      do_rating=true
-
-     do_ipv6_only=false
-     do_ipv4_only=false
 }
 
 # returns number of $do variables set = number of run_funcs() to perform