bcc: Use bpf_probe_read_str to read tracepoint data_loc field
bcc: Use bpf_probe_read_str to read tracepoint data_loc field

The data_loc field (defined as __string in kernel source) should
be treated as string NOT a fixed-size array, add a new macro
TP_DATA_LOC_READ_STR which use bpf_probe_read_str to reflect this.

Signed-off-by: Hengqi Chen <2146682b4c3fe4aa97c809745b7d5be9e6165e06@outlook.com>

iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc,brendangregg/bcc,brendangregg/bcc,brendangregg/bcc,brendangregg/bcc