Fix compilation on systems with larger utsname field sizes

[ellert]

On Linux the sizes of the sysname and machine fields are 65 bytes and the target array is large enough to hold the result of the snprintf command.

On platforms where the sizes of the fields are larger, e.g. GNY/Hurd where they are 1024 bytes, the results overflows.

src/request.c:1105:57: error: ‘%s’ directive output may be truncated writing up to 2048 bytes into a region of size between 211 and 218 [-Werror=format-truncation=]

This change does not change the size of the array on Linux: 126 + 65 + 65 = 256