CLEANUP: mux-h1: Rename H1C_F_ERR_PENDING into H1C_F_ABRT_PENDING

CLEANUP: mux-h1: Rename H1C_F_ERR_PENDING into H1C_F_ABRT_PENDING

H1C_F_ERR_PENDING flags will be used to refactor error handling at the H1
connection level. It will be used to notify error during sends. Thus, the
flag to notify an error must be sent before closing the connection is now
named H1C_F_ABRT_PENDING.

This introduce a naming convertion: ERROR must be used to notify upper layer
of an event at the lower ones while ABORT must be used in the opposite
direction.