msm: ipa: add a check for header len when adding a header to ipa

The procedure which adds a header to the IPA was missing a boundary
check, causing a potential buffer overflow.

CRs-fixed: 791163
Change-Id: I4c372369feba1df68364a7c7b406e735147932d7
Acked-by: David Arinzon <darinzon@qti.qualcomm.com>
Signed-off-by: Sivan Reinstein <sivanr@codeaurora.org>