misc: fix pcap [rx|tx|drop] filename stem overflow
misc: fix pcap [rx|tx|drop] filename stem overflow

Type: fix

Change-Id: I2b6b7b6f28cbf7accf883743e390b0031dd13bbb
Signed-off-by: Benoît Ganne <38aad8ffcfa407b890d258e568f161530f66882d@cisco.com>

chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp