trace: events: cleanup deprecated strncpy uses

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

For 2 out of 3 of these changes we can simply swap in strscpy() as it
guarantess NUL-termination which is needed for the following trace
print.

trace_rpcgss_context() should use memcpy as its format specifier %.*s
allows for the length to be specifier (__entry->len). Due to this,
acceptor does not technically need to be NUL-terminated. Moreover,
swapping in strscpy() and keeping everything else the same could result
in truncation of the source string by one byte. To remedy this, we could
use `len + 1` but I am unsure of the size of the destination buffer so a
simple memcpy should suffice.
|	TP_printk("win_size=%u expiry=%lu now=%lu timeout=%u acceptor=%.*s",
|		__entry->window_size, __entry->expiry, __entry->now,
|		__entry->timeout, __entry->len, __get_str(acceptor))

I suspect acceptor not to naturally be a NUL-terminated string due to
the presence of some stringify methods.
|	.crstringify_acceptor	= gss_stringify_acceptor,

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20240401-strncpy-include-trace-events-mdio-h-v1-1-9cb5a4cda116@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>