net: msm_rmnet.h: Fix data type of flow_id in QoS header

Fix an issue where the flow_id was appearing to be 8 bytes in
64 bit platforms. This is because the flow_id is declared as unsigned
long which is 8 bytes in 64 bit and 4 bytes in 32 bit platforms.
Change the flow_id to uint32_t to make it 4 bytes on all platforms.

CRs-fixed: 663814
Change-Id: I2472fb99750d1818ecfae03b5bcd860f19ac51a7
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>