net: fix checksum API documentation
net: fix checksum API documentation

Minor corrections and improvements to documentation
for checksum APIs.

Fixes: 6006818cfb26 ("net: new checksum functions")
Fixes: 45a08ef55e44 ("net: introduce functions to verify L4 checksums")
Cc: stable@dpdk.org

Signed-off-by: Lance Richardson <4e26776f5588f0e1c0c16cd2ddc0e9efc79c5b3a@broadcom.com>
Acked-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk