vsftpd: fix bug related to option conf_file #21466

Job	Run time
Feeds Package Test Build / Test aarch64_generic	10m 41s
Feeds Package Test Build / Test arm_cortex-a15_neon-vfpv4	11m 34s
Feeds Package Test Build / Test arm_cortex-a9_vfpv3-d16	11m 5s
Feeds Package Test Build / Test i386_pentium-mmx	12m 22s
Feeds Package Test Build / Test mips_24kc	10m 10s
Feeds Package Test Build / Test mipsel_24kc	11m 15s
Feeds Package Test Build / Test powerpc_464fp	10m 22s
Feeds Package Test Build / Test powerpc_8548	10m 11s
Feeds Package Test Build / Test riscv64_riscv64	11m 1s
Feeds Package Test Build / Test x86_64	11m 33s
	1h 50m 14s

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