vlr: fix IMEI length

Set the length of vlr_subscr->imei to
	GSM23003_IMEI_NUM_DIGITS_NO_CHK (14)
instead of
	GSM23003_IMEISV_NUM_DIGITS (16).

Note that there is also GSM23003_IMEI_NUM_DIGITS (15), which includes
an additional checksum digit. This digit is not intended for digital
transmission, so we don't need to store it. Also by not storing it, we
can simply copy the IMEI-part from the IMEISV to the IMEI without
worrying about the checksum (will be done in a follow up patch).

A good overview of the IMEI/IMEISV structure is here:
https://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity#Structure_of_the_IMEI_and_IMEISV_(IMEI_software_version)

Related: OS#2542
Change-Id: Iaf2569c099874b55acbd748b776394726cc5ce54
7 files changed