bhyve: Document that MAC address has to be unicast

bhyve accepts any MAC address even foreign as long it is a unicast one.

Reviewed by:	ziaee
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D54372

usr.sbin/bhyve/bhyve.8

@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd December 23, 2025
+.Dd December 26, 2025
 .Dt BHYVE 8
 .Os
 .Sh NAME
@@ -551,6 +551,7 @@ If
 is not specified, the MAC address is derived from a fixed OUI, and the
 remaining bytes from an MD5 hash of the slot and function numbers and
 the device name.
+If specified, it must be a unicast MAC address.
 .Pp
 The MAC address is an ASCII string in
 .Xr ethers 5

usr.sbin/bhyve/bhyve_config.5

@@ -517,8 +517,10 @@ Intel e82545 network interfaces support the following variables:
 .It Sy Name Ta Sy Format Ta Sy Default Ta Sy Description
 .It Va mac Ta MAC address Ta generated Ta
 MAC address.
-If an explicit address is not provided,
-a MAC address is generated from a hash of the device's PCI address.
+If not specified, the MAC address is derived from a fixed OUI, and the
+remaining bytes from an MD5 hash of the slot and function numbers and
+the device name.
+If specified, it must be a unicast MAC address.
 .El
 .Ss Frame Buffer Settings
 .Bl -column "password" "[IP:]port" "127.0.0.1:5900"
@@ -746,8 +748,10 @@ VirtIO network interfaces support the following variables:
 .It Sy Name Ta Sy Format Ta Sy Default Ta Sy Description
 .It Va mac Ta MAC address Ta generated Ta
 MAC address.
-If an explicit address is not provided,
-a MAC address is generated from a hash of the device's PCI address.
+If not specified, the MAC address is derived from a fixed OUI, and the
+remaining bytes from an MD5 hash of the slot and function numbers and
+the device name.
+If specified, it must be a unicast MAC address.
 .It Va mtu Ta integer Ta 1500 Ta
 The largest supported MTU advertised to the guest.
 .El