cxgbe(4): sysctls to display the TOE's TCP timers.

cask:~# sysctl -d dev.t5nex.0.toe
dev.t5nex.0.toe.finwait2_timer: FINWAIT2 timer (us)
dev.t5nex.0.toe.initial_srtt: Initial SRTT (us)
dev.t5nex.0.toe.keepalive_intvl: Keepidle interval (us)
dev.t5nex.0.toe.keepalive_idle: Keepidle idle timer (us)
dev.t5nex.0.toe.persist_max: Persist timer max (us)
dev.t5nex.0.toe.persist_min: Persist timer min (us)
dev.t5nex.0.toe.rexmt_max: Retransmit max (us)
dev.t5nex.0.toe.rexmt_min: Retransmit min (us)
dev.t5nex.0.toe.dack_timer: DACK timer (us)
dev.t5nex.0.toe.dack_tick: DACK tick (us)
dev.t5nex.0.toe.timestamp_tick: TCP timestamp tick (us)
dev.t5nex.0.toe.timer_tick: TP timer tick (us)
...

cask:~# sysctl dev.t5nex.0.toe
dev.t5nex.0.toe.finwait2_timer: 9765440
dev.t5nex.0.toe.initial_srtt: 244128
dev.t5nex.0.toe.keepalive_intvl: 73240800
dev.t5nex.0.toe.keepalive_idle: 7031116800
dev.t5nex.0.toe.persist_max: 9765440
dev.t5nex.0.toe.persist_min: 976544
dev.t5nex.0.toe.rexmt_max: 9765440
dev.t5nex.0.toe.rexmt_min: 244128
dev.t5nex.0.toe.dack_timer: 19520
dev.t5nex.0.toe.dack_tick: 32.768
dev.t5nex.0.toe.timestamp_tick: 1048.576
dev.t5nex.0.toe.timer_tick: 32.768
...