Bugfixes: match field masks, ICMPv4 TYPE match, Clear-Actions instruction, duplicate match fields segfault

ICMPv4 TYPE match was incorrectly using CODE enum value.

Match fields with masks had the wrong length on the wire, consequently causing receiver of flowmod msg to return an OpenFlow error:     Type: OFPET_BAD_MATCH (4)  Code: OFPBMC_BAD_FIELD (6)
Proposed fix here is to double the OXMTLV length when has_mask is true.