mta: replace rand() calls with calls to common_rand() (Coverity CID 98101)
mta: replace rand() calls with calls to common_rand() (Coverity CID 98101)

cmail-mta/cmail,cmail-mta/cmail,cmail-mta/cmail,cmail-mta/cmail,cmail-mta/cmail,cmail-mta/cmail