BUG/MINOR: http-fetch: Use integer value when possible in "method" sample fetch

BUG/MINOR: http-fetch: Use integer value when possible in "method" sample fetch

Because of the previous fix, if the HTTP parsing is performed when the
"method" sample fetch is called, we always rely on the string representation
of the request method.

Indeed, if no parsing was performed when the "method" sample fetch is
called, the transaction method is HTTP_METH_OTHER because it was just
initialized. However, without this patch, in this case, we always retrieve
the method by reading the request start-line.

Now, when the method is HTTP_METH_OTHER, we systematically try to parse the
request but the method is tested once again after the parsing to be able to
use the integer representation when possible.

This patch must be backported as far as 2.0.