tcp: inline tcp_chrono_start()

tcp: inline tcp_chrono_start()

tcp_chrono_start() is small enough, and used in TCP sendmsg()
fast path (from tcp_skb_entail()).

Note clang is already inlining it from functions in tcp_output.c.

Inlining it improves performance and reduces bloat :

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/2 grow/shrink: 1/0 up/down: 1/-84 (-83)
Function                                     old     new   delta
tcp_skb_entail                               280     281      +1
__pfx_tcp_chrono_start                        16       -     -16
tcp_chrono_start                              68       -     -68
Total: Before=25192434, After=25192351, chg -0.00%

Note that tcp_chrono_stop() is too big.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20260308123549.2924460-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>