BUG/MINOR: http-ana: Set method to HTTP_METH_OTHER when an HTTP txn is created

BUG/MINOR: http-ana: Set method to HTTP_METH_OTHER when an HTTP txn is created

This patch is required to fix "method" sample fetch. But it make sense to
initialize the method of an HTTP transaction to HTTP_METH_OTHER. This way,
before the request parsing, the method is considered as unknown except if we
are able to retrieve the request start-line. It is especially important for
TCP streams.

About the "method" sample fetch, this patch is a way to be sure no random
method is returned when the sample fetch is used on a TCP stream before any
HTTP parsing.

This patch must be backported as far as 2.0.