Turnkey SMB server performance tweaks

From Arch, https://wiki.archlinux.org/title/Samba#Improve_throughput

deadtime = 30
use sendfile = yes
min receivefile size = 16384
socket options = IPTOS_LOWDELAY TCP_NODELAY IPTOS_THROUGHPUT SO_RCVBUF=131072 SO_SNDBUF=131072

Old, wrong:

write cache size = 2097152
min receivefile size = 16384
getwd cache = true