lib:replace: Avoid overlapping strncpy calls, replace with memmove

In bsd_attr_list() buffers that can overlap are copied using strncpy, but this is undefined behavior, and is now detected in FreeBSD after samba started to be built with _FORTIFY_SOURCE=3. This results in a SIGABRT as soon as any extended attributes are processed:

#0  kill () at kill.S:4
#1  0x0000000800ccb121 in __fail (msg=0x800bd0a20 "buffer overflow detected; terminated") at /usr/src/lib/libc/secure/libc_stack_protector.c:119
#2  0x0000000800ccb140 in __chk_fail () at /usr/src/lib/libc/secure/libc_stack_protector.c:132
#3  0x0000000800ccaf03 in __strncpy_chk (dst=0x217a <error: Cannot access memory at address 0x217a>, src=0x6 <error: Cannot access memory at address 0x6>, len=0, slen=<optimized out>) at /usr/src/lib/libc/secure/strncpy_chk.c:50
#4  0x0000000800586825 in __strncpy_ichk (dst=0x7fffffffc2d5 "", src=0x7fffffffc2db "org.netatalk.Metadata$org.netatalk.has-Extended-Attributes", len=21) at /usr/include/ssp/string.h:120
#5  bsd_attr_list (type=0, arg=..., list=0x7fffffffc2d5 "", size=1024) at ../../lib/replace/xattr.c:284

Replace the strncpy calls with memmove, since in this particular case the result is equivalent.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• (optional) This MR is just one part towards a larger feature.
• (optional, if backport required) Bugzilla bug filed and BUG: tag added
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code