net/samba41[36]: Make 'USES=shebangfix' work as is expected

While testing patch submitted to bug #270383, I noticed
'USES=shebangfix' doesn't work as is expected with current samba
ports. According to the investigation by Tatsuki Makino, it is because
SHEBANG_FILES is defined after bsd.port.options.mk and bsd.port.pre.mk
are included. So fix the issue by moving the definition before the
inclusion of them

Reference: https://lists.freebsd.org/archives/freebsd-ports/2023-November/004849.html
Reference: https://lists.freebsd.org/archives/freebsd-ports/2023-November/004852.html
Reference: https://lists.freebsd.org/archives/freebsd-ports/2023-November/004853.html
PR: 274885
Approved by: maintainer timeout