DF-3279 fix validation run — FIXED kernel #1 (bridge_delete_span frees
bif->bif_info).

Commands:
    ifconfig tap0 create; ifconfig bridge0 create
    vmstat -m | grep -E "^ *devbuf"
    ./span_leak 20000
    vmstat -m | grep -E "^ *devbuf"

Output:
             devbuf     236    266K       0    390M      347
    (20000 spanport add/del cycles)
             devbuf     236    266K       0    390M    39.4K

devbuf in-use: 266K -> 266K (ZERO growth; requests counter rises because
the allocations still happen, but they are now freed).

BASELINE (stock kernel): 3.12M -> 5.40M (+2.28MB / 20000 cycles
= ~114 bytes leaked per cycle = one bridge_ifinfo per span add/del).