Compiler warning fixes

snra-server-client.c: In function 'snra_server_client_io_cb':
snra-server-client.c:303:7: warning: implicit declaration of function 'memmove' [-Wimplicit-function-declaration]
snra-server-client.c:303:7: warning: incompatible implicit declaration of built-in function 'memmove' [enabled by default]
snra-server-client.c: In function 'write_fragment':
snra-server-client.c:582:5: warning: implicit declaration of function 'memcpy' [-Wimplicit-function-declaration]
snra-server-client.c:582:5: warning: incompatible implicit declaration of built-in function 'memcpy' [enabled by default]