When 'check-imei-rqd 1 early' is set in the config, send the IMEI to
the HLR before doing the location update with the HLR.
The OsmoHLR documentation referenced in the code will be added in
osmo-hlr.git's Change-Id I2dd4a56f7b8be8b5d0e6fc32e04459e5e278d0a9.
Related: OS#2542
Change-Id: I88283cad23793b475445d814ff49db534cb41244
Original libvlr code is by Harald Welte <laforge@gnumonks.org>,
polished and tweaked by Neels Hofmeyr <nhofmeyr@sysmocom.de>.
This is a long series of trial-and-error development collapsed in one patch.
This may be split in smaller commits if reviewers prefer that. If we can keep
it as one, we have saved ourselves the additional separation work.
Related: OS#1592
Change-Id: Ie303c98f8c18e40c87c1b68474b35de332033622