shells/scponly: fix segfault on FreeBSD 11

Patch introduced in r493861 to fix segfault on FreeBSD 12+ broke it on
FreeBSD 11. This new version fixes it on both versions.

While here, pet portlint a bit moving USES to proper place and removing
RUN_DEPENDS := BUILD_DEPENDS adding individual run depends where it's
necessary.

PR: 235810
Submitted by: Stewart Morgan <stewart.morgan@gmail.com>
Sponsored by: Rubicon Communications, LLC (Netgate)