msm: ipa: fix hdr table full condition

The header table is managed by IPA driver and header cannot be
moved. Instead a "free list" is maintained for deleted headers.
This change fixes a bug on header addition where the table is considered
full only if it is full and the free list is empty.

Change-Id: Ief8a384ea105c6f0179faaf95a98b9731fe6a01e
CRs-Fixed: 2048799
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>