Improved the capabilities feature detection. Previously included file sys/capability.h mentioned in capset(2) man page, belongs to the libcap-dev package, which may not be installed on some Linux systems when compiling nginx. This prevented the capabilities feature from being detected and compiled on that systems. Now linux/capability.h system header is included instead. Since capset() declaration is located in sys/capability.h, now capset() syscall is defined explicitly in code using the SYS_capset constant, similarly to other Linux-specific features in nginx.

--- a/src/os/unix/ngx_linux_config.h
+++ b/src/os/unix/ngx_linux_config.h
@@ -100,7 +100,7 @@ typedef struct iocb  ngx_aiocb_t;
 
 
 #if (NGX_HAVE_CAPABILITIES)
-#include <sys/capability.h>
+#include <linux/capability.h>
 #endif