[lib][pktbuf] fix a warning on the no-vm path
[lib][pktbuf] fix a warning on the no-vm path

srodrig1/lk,nvll/lk,sndnvaps/lk,ErikCorryGoogle/lk,hollanderic/lkstuff,hollanderic/lkstuff,nvll/lk,minglun-tsai/lk,skabet/lk,sndnvaps/lk,travisg/lk,skabet/lk,minglun-tsai/lk,sndnvaps/lk,littlekernel/lk,ErikCorryGoogle/lk,nvll/lk,srodrig1/lk,srodrig1/lk,hollanderic/lkstuff,sndnvaps/lk,minglun-tsai/lk,travisg/lk,hollanderic/lkstuff,sndnvaps/lk,littlekernel/lk,srodrig1/lk,skabet/lk,nvll/lk,minglun-tsai/lk,travisg/lk,travisg/lk,ErikCorryGoogle/lk,srodrig1/lk,littlekernel/lk,nvll/lk,skabet/lk,skabet/lk,littlekernel/lk,ErikCorryGoogle/lk