msm: ipa3: Add mutex to prevent race condition

There is a race condition between ipa3_nat_init_cmd
and ipa_read_nat4. The two thread will R/W the critical
global variables. This will result in race conditions
and possibly buffer overread/ overwrite issues. Add code
to prevent this race condition.

Change-Id: I6bf9a837ae941cf3ad9413da6e44821916acf196
Acked-by: Pooja Kumari <kumarip@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>