nFAPI/VNF: Correctly set message length when segmenting

The 5G nFAPI message length is 32bits. In particular tx_data.requests
can be longer than 64kB. When segmenting, we should correctly write the
message of the current segment (across all 32bits), because the
length would interpreted wrongly otherwise.

This fixes a bug in which tx_data.requests were discarded for 4-layer DL
MIMO on 100 MHz with this message:

    P7 unpack message length is greater than the message buffer

Further, increase the type of various (segment-related) variables to 32
bits. Currently, the maximum segment size is sxt to 65000 bytes (and in
will likely remain, because the maximum UDP size is 65536);
nevertheless, increase it in case we will ever go beyond this.

See also commit dee68e6319 ("nFAPI: increase maximum segment size to
65000")

nfapi/open-nFAPI/vnf/public_inc/nfapi_vnf_interface.h

@@ -669,8 +669,8 @@ typedef struct nfapi_vnf_p7_config
 	uint8_t checksum_enabled;
 
 	/*! The maxium size of a P7 segement. If a message is large that this it
-	 * will be segemented */
-	uint16_t segment_size;
+	 * will be segmented. Note: u32 to cover 4G and 5G. */
+	uint32_t segment_size;
 	uint16_t max_num_segments;
 
 	/*! Configuration option for the p7 pack unpack functions*/