Fix compiling issue with GCC-8.x in string test functions
Fix compiling issue with GCC-8.x in string test functions

Same pointer is passed to two or more restrict-qualified parameters of a function.

vpp/src/plugins/unittest/string_test.c: In function ‘test_strcpy_s’:
vpp/src/plugins/unittest/string_test.c:562:19: error: passing argument 1 to restrict-qualified parameter aliases with argument 3 [-Werror=restrict]
err = strcpy_s (dst, s1size, dst);
^~~ ~~~

Change-Id: Ica06b457bbcbf2d552eec380976c37f9fd447b1c
Signed-off-by: Lijian Zhang <5bf702a4364390af4958a9b6773dbd5c19bc4226@arm.com>
Reviewed-by: Sirshak Das <52b659a5c3604c18da7b4f485dd9254e5f624e3a@arm.com>

chrisy/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp