bnxt: Do not read past the end of test names

In the Linux kernel, the following vulnerability has been resolved:

bnxt: Do not read past the end of test names

Test names were being concatenated based on a offset beyond the end of

the first name, which tripped the buffer overflow detection logic:

detected buffer overflow in strnlen

[...]

Call Trace:

bnxt_ethtool_init.cold+0x18/0x18

Refactor struct hwrm_selftest_qlist_output to use an actual array,

and adjust the concatenation to use snprintf() rather than a series of

strncat() calls.