net: Space: Replace memset(0) + strscpy() with strscpy_pad()

Replace memset(0) followed by strscpy() with strscpy_pad() to improve
netdev_boot_setup_add(). This avoids zeroing the memory before copying
the string and ensures the destination buffer is only written to once,
simplifying the code and improving efficiency.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20250814180514.251000-2-thorsten.blum@linux.dev


Signed-off-by: Jakub Kicinski <kuba@kernel.org>