add osmo_gsup_msgb_alloc()

Throughout osmo-hlr's code, the GSUP msgb allocation is duplicated as:

  msgb_alloc_headroom(1024+16, 16, "foo");

Instead, use one common function to keep the magic numbers in one place.

Change-Id: I40e99b5bc4fd8f750da7643c03b2119ac3bfd95e
5 files changed