MINOR: http: switch the http state to an enum

MINOR: http: switch the http state to an enum

This reduces its size which is not reused by anything else. However it
will significantly improve the debugger's output since we'll now get
real state values.

The default case had to be enabled in the parsers because gcc tries
to optimize the switch/case and noticed some values were missing from
the enums and emitted a warning.