file: /proc/sys/net/ipv4/tcp_min_tso_segs
variable: net.ipv4.tcp_min_tso_segs
Official reference

Minimal number of segments per TSO frame. Since linux-3.12, TCP does an automatic sizing of TSO frames, depending on flow rate, instead of filling 64Kbytes packets. For specific usages, it’s possible to force TCP to build big TSO frames. Note that TCP stack might split too big TSO packets if available window is too small. Default: 2