l3_learning: Fix lost packet expiration
l3_learning: Fix lost packet expiration

The tuple used to index the lost packet buffer was documented
backwards, and used backwards in one place.  This fixes that.

The outstanding ARP buffer's index tuple was also documented
backwards (though apparently only ever used correctly), and
this fixes that too.

Totally untested.  Bug reported by wyanan@mail.ustc.edu.cn

kavitshah8/SDNDeveloper,kavitshah8/SDNDeveloper,kulawczukmarcin/mypox,kulawczukmarcin/mypox,PrincetonUniversity/pox,kpengboy/pox-exercise,kpengboy/pox-exercise,pthien92/sdn,VamsikrishnaNallabothu/pox,xAKLx/pox,andiwundsam/_of_normalize,carlye566/IoT-POX,diogommartins/pox,adusia/pox,carlye566/IoT-POX,adusia/pox,diogommartins/pox,jacobq/csci5221-viro-project,jacobq/csci5221-viro-project,xAKLx/pox,PrincetonUniversity/pox,MurphyMc/pox,jacobq/csci5221-viro-project,xAKLx/pox,andiwundsam/_of_normalize,pthien92/sdn,noxrepo/pox,waltznetworks/pox,PrincetonUniversity/pox,denovogroup/pox,diogommartins/pox,MurphyMc/pox,PrincetonUniversity/pox,denovogroup/pox,MurphyMc/pox,xAKLx/pox,chenyuntc/pox,noxrepo/pox,chenyuntc/pox,adusia/pox,VamsikrishnaNallabothu/pox,adusia/pox,carlye566/IoT-POX,diogommartins/pox,xAKLx/pox,kulawczukmarcin/mypox,pthien92/sdn,jacobq/csci5221-viro-project,andiwundsam/_of_normalize,kpengboy/pox-exercise,PrincetonUniversity/pox,denovogroup/pox,chenyuntc/pox,waltznetworks/pox,chenyuntc/pox,kavitshah8/SDNDeveloper,noxrepo/pox,MurphyMc/pox,kulawczukmarcin/mypox,andiwundsam/_of_normalize,carlye566/IoT-POX,carlye566/IoT-POX,waltznetworks/pox,adusia/pox,waltznetworks/pox,pthien92/sdn,denovogroup/pox,noxrepo/pox,denovogroup/pox,kpengboy/pox-exercise,kavitshah8/SDNDeveloper,pthien92/sdn,waltznetworks/pox,VamsikrishnaNallabothu/pox,diogommartins/pox,VamsikrishnaNallabothu/pox,VamsikrishnaNallabothu/pox,kulawczukmarcin/mypox,kpengboy/pox-exercise,MurphyMc/pox,jacobq/csci5221-viro-project,chenyuntc/pox