security/ipv6toolkit: fix build on 14-CURRENT on amd64

This fixes the following on 14-CURRENT on amd64:

ld: error: can't create dynamic relocation R_X86_64_32S against local
symbol in readonly segment; recompile object files with -fPIC or pass
'-Wl,-z,notext' to allow text relocations in the output

defined in /wrkdirs/usr/ports/security/ipv6toolkit/work/ipv6toolkit-v2.0/libipv6/libipv6.a(libipv6.o)
referenced by libipv6.c

libipv6.o:(is_service_port) in archive /wrkdirs/usr/ports/security/ipv6toolkit/work/ipv6toolkit-v2.0/libipv6/libipv6.a

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