capdump: store suffix and remove limitation

Within the same run the suffix will be recorded so the lookup will be fast and doesn't need a limitation. If it overrides previous files it might take some time to find the first available it but it probably won't be an issue (e.g. large number of files with the same pattern)
capdump: fix potential buffer overflow
capmerge: workaround for const warning
format: parse MPLS header
format: support pseudo-wire control word (eth over MPLS)