improve partner-port check in createTtpPortMapping

improve partner-port check in createTtpPortMapping

use the checkPartnerPort method inside createTtpPortMapping
such as done in createXpdrPortMapping or createPpPortMapping.

Beyond the overall coherency, this allows to perform some additional
(and maybe missing) null checking before accessing the related fields
and it also improves the log messages details.

JIRA: TRNSPRTPCE-353
Signed-off-by: guillaume.lambert <guillaume.lambert@orange.com>
Change-Id: Ibe90c2d9755ff981762da0cc179e367882f3fa33
(cherry picked from commit d356e7d288af388774773eaea7ea64d66de9bab4)