[REFACTORING] Merging validation logic from Xapi_pif.{introduce,introduce_internal} into Xapi_pif.{introduce_internal}.
[REFACTORING] Merging validation logic from Xapi_pif.{introduce,introduce_internal} into Xapi_pif.{introduce_internal}.

Signed-off-by: Jonathan Knowles <47466d50a94574c6fb872a0e5feec104dcb68f29@eu.citrix.com>

johnelse/xcp-rrdd,djs55/xcp-networkd,koushikcgit/xcp-rrdd,johnelse/xcp-rrdd,djs55/xcp-rrdd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-networkd,djs55/xcp-networkd,robhoes/squeezed,koushikcgit/xcp-networkd,sharady/xcp-networkd,djs55/squeezed,koushikcgit/xcp-rrdd,koushikcgit/xcp-rrdd,djs55/xcp-rrdd,sharady/xcp-networkd,simonjbeaumont/xcp-rrdd