msgb: assert msgb->lXh to be not NULL

When any of l1h, l2h, l2h or l4h is set to NULL (which is the default
for newly allocated message buffers). Then the msgb_lXhlen() functions
will return the address value of msgb->tail. This can lead to unexpected
results at a later point. We should have an OSMO_ASSERT to catch the
problem early.

Change-Id: I1795c559f190713ebbabfbabf3453ab77da46a49
Related: OS#5645
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M include/osmocom/core/msgb.h
1 file changed, 4 insertions(+), 0 deletions(-)