Tested the two sysctls' output before and after the change.
before
root@s1:~ # sysctl -d net.inet.tcp.bb.disable_all
net.inet.tcp.bb.disable_all: Disable all BB logging for all connections
root@s1:~ # sysctl net.inet.tcp.bb.disable_all
net.inet.tcp.bb.disable_all: 0
iroot@s1:~ # sysctl -d net.inet.tcp.bb.log_auto_mode
net.inet.tcp.bb.log_auto_mode: Logging mode for auto-selected sessions (default is TCP_LOG_STATE_HEAD_AUTO)
root@s1:~ # sysctl net.inet.tcp.bb.log_auto_mode
net.inet.tcp.bb.log_auto_mode: 1
after
root@s1:~ # sysctl -d net.inet.tcp.bb.disable_all
net.inet.tcp.bb.disable_all: Disable all BB logging for all connections
root@s1:~ # sysctl net.inet.tcp.bb.disable_all
net.inet.tcp.bb.disable_all: 0
root@s1:~ # sysctl -d net.inet.tcp.bb.log_auto_mode
net.inet.tcp.bb.log_auto_mode: Logging mode for auto-selected sessions (default is TCP_LOG_STATE_TAIL)
root@s1:~ # sysctl net.inet.tcp.bb.log_auto_mode
net.inet.tcp.bb.log_auto_mode: 1