setfib.2: Note that the number of FIBs can be adjusted after boot

Reviewed by:	zlei, imp
MFC after:	2 weeks
Sponsored by:	Klara, Inc.
Sponsored by:	Stormshield
Differential Revision:	https://reviews.freebsd.org/D48545

lib/libsys/setfib.2

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd March 19, 2012
+.Dd January 10, 2025
 .Dt SETFIB 2
 .Os
 .Sh NAME
@@ -55,15 +55,20 @@ The system maximum is set in the kernel configuration file with
 .Pp
 or in
 .Pa /boot/loader.conf
+or
+.Pa /etc/sysctl.conf
 with
 .Pp
 .Dl net.fibs= Ns Qq Em N
 .Pp
 where
 .Em N
-is an integer.
-This maximum is capped at 65536 due to the implementation storing
-the fib number in a 16-bit field in the
+is an integer smaller than 65536.
+Note that the number of FIBs may be increased after booting, but cannot be
+reduced.
+.Pp
+The maximum of 65536 is due to the implementation storing
+the FIB number in a 16-bit field in the
 .Xr mbuf 9
 packet header, however it is not suggested that one use such a large number
 as memory is allocated for every FIB regardless of whether it is used, and